JP4047522B2

JP4047522B2 - Wireless terminal device

Info

Publication number: JP4047522B2
Application number: JP2000211357A
Authority: JP
Inventors: 浩二田島
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2000-07-12
Filing date: 2000-07-12
Publication date: 2008-02-13
Anticipated expiration: 2020-07-12
Also published as: JP2002027518A

Description

【０００１】
【発明の属する技術分野】
本発明は、基地局と組合わされて無線通信網を構成する無線端末装置に関する。
【０００２】
【従来の技術】
無線端末装置であるパーソナルハンディホンシステム（以後、ＰＨＳと呼ぶ）は、基地局の電磁波の届く範囲が狭い小ゾーン方式であるので、１つの基地局と通信できる範囲が、半径１００〜５００ｍ程度と小さい。したがって、ＰＨＳの通信中に移動する場合には、１つの基地局から隣接する基地局に通信を引継ぐ処理（以後、ハンドオーバと呼ぶ）が行われる。
【０００３】
ハンドオーバには、基地局から移動局であるＰＨＳに対して、ハンドオーバを要求してくる場合と、ＰＨＳが通信中の信号の受信電界強度を測定し、基地局から指定された受信電界強度（再発呼型ハンドオーバ保持レベル）以下になったことを判断して、ハンドオーバ処理を行う２種類がある。いずれの場合にも、ハンドオーバを開始するときに周辺基地局の受信電界強度の測定を行い、受信した基地局の中から受信電界強度が最も高い基地局を選択してハンドオーバを行う。
【０００４】
第二世代コードレス電話システム標準規格ＲＣＲＳＴＤ−２８で規定されているハンドオーバ処理では、前記のように受信した基地局の中から受信電界強度が最も高いことを判断基準として基地局を選択してハンドオーバを行う。ＰＨＳの利用者が、停止および歩行程度の速度で移動中であれば、受信電界強度が最も高いことを判断基準として基地局を選択しても特に通信上の問題はないけれども、ＰＨＳの利用者が、歩行速度を超える速い速度、たとえば自動車や列車などで移動している場合には、受信電界強度が最も高いことを判断基準として選択した基地局が、ＰＨＳ利用者の進行方向と逆の方向にあると、ハンドオーバ先として選択した基地局の受信電界強度が、ＰＨＳ利用者の移動にともなって急速に減少するので、ハンドオーバができなかったり、ハンドオーバができても、すぐに別の基地局にハンドオーバしなければならないという問題があった。
【０００５】
このようなハンドオーバ先の基地局選択基準を最も高い受信電界強度のみにおくことの問題点を解決するための先行技術として、特開平８−１５４２６４号公報が開示されている。この先行技術では、周辺基地局からの送信される受信電界強度を記憶し、一定時間後における受信電界強度との比較を行い、受信電界強度の差が所定値を超える基地局を発見した場合には、その基地局をハンドオーバ先として選択し、いずれの基地局も受信電界強度の差が所定値以下である場合には、各基地局ごとに時系列的に受信電界強度の変化を求めて、受信電界強度の時系列的な変化量が最も大きい基地局をハンドオーバ先として選択する。
【０００６】
【発明が解決しようとする課題】
この先行技術のハンドオーバ処理には以下の問題がある。周辺基地局の受信電界強度を記憶し、一定時間後の受信電界強度との受信電界強度差を求め、受信電界強度差が所定値を超える基地局を発見すれば、現在通信中の受信電界強度が高く、通信状態が良好であってもハンドオーバを行うので、必要のないハンドオーバを行うことがあり、不要にハンドオーバ回数を増加させる。また、周辺基地局の受信電界強度差がいずれも所定値以下である場合には、受信電界強度の絶対値にかかわらず、受信電界強度の時系列的な変化量を基準としてハンドオーバ先の基地局を選択するので、選択したハンドオーバ先の基地局の受信電界強度が、現在通信中の基地局の受信電界強度よりも低くなることが起こる。
【０００７】
ＰＨＳは、移動しながら利用されることが多く、ハンドオーバ先として選択した基地局の受信電界強度が低いと、ＰＨＳの移動先の周辺環境によって電磁波の受信電界強度が時間的に変動する、いわゆるフェージングの影響を受けて、雑音を生じ通話品質が低下するおそれがある。通話品質の低下が起これば、基地局からハンドオーバの要求が出されて、ハンドオーバ回数が増すことになる。また、受信電界強度の時系列的な変化量を基準とするハンドオーバ先基地局の選択は、ＰＨＳ利用者の移動先を予測してハンドオーバ先基地局を選択するということである。ＰＨＳ利用者の移動先予測が、受信電界強度の時系列的な変化量を基準とした予測と合わなかった場合には、受信電界強度が予測とは異なり低い電界強度となるので、再度ハンドオーバを行わなければならなくなり、必ずしもハンドオーバ回数の低減にはつながらない。さらに、現在通信中の通話状態とは関係なく所定の時間ごとに周辺基地局の受信電界強度の測定を繰返すので、たとえばＰＨＳ利用者が停止している状態で受信電界強度が高く通話品質もよい場合には、無駄な動作を行い余分な電力を消費することになり、電池を消耗させて通話時間を減少させるという影響がある。
【０００８】
本発明は、通話時間および通話品質への影響が少なく、移動中に最適な基地局にハンドオーバすることのできる無線端末装置を提供する。
【０００９】
【課題を解決するための手段】
本発明は、複数の相互に異なる固定位置に設けられた各基地局との通信を行なう無線端末装置において、
複数の基地局から送信される信号の受信電界強度を測定する受信電界強度測定手段と、
測定した受信電界強度と予め定める基準値および基準値に所定値を加算した値とを比較する手段と、
比較手段の出力に応答し、通信中の基地局から送信される信号の受信電界強度が、基準値を超え基準値に所定値を加算した値以下であるとき、各基地局から送信される信号の受信電界強度を第１受信電界強度としてストアし、通信中の基地局から送信される信号の受信電界強度が、基準値以下であるとき、各基地局から送信される信号の受信電界強度を第２受信電界強度としてストアする手段と、
第１受信電界強度よりも第２受信電界強度が大きい基地局を選び、さらに第１受信電界強度よりも第２受信電界強度が大きい基地局のうちで、第２受信電界強度が最大である基地局を選択する手段と、
通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値を超えるとき、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わせずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値以下であるとき、基地局測定禁止中であるか否かを判断し、基地局測定禁止中であれば、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、基地局測定禁止中でなければ、複数の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせて、各基地局から送信される信号の受信電界強度をストア手段にストアさせ、一定時間の基地局測定禁止の状態を設定した後、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせる手段とを含むことを特徴とする無線端末装置である。
【００１０】
本発明に従えば、通信中の基地局から送信される信号の受信電界強度と予め定める基準値および基準値に所定値を加算した値とを比較する。基準値としては、たとえばハンドオーバを必要とする臨界の受信電界強度が設定され、所定値としては、たとえば１０ｄＢμＶが設定される。比較結果の出力に応答し、通信中の基地局から送信される信号の受信電界強度が基準値に所定値を加算した値を超えるとき、各基地局から送信される受信電界強度を測定することなく通信中の基地局との通信を継続し、通信中の基地局から送信される信号の受信電界強度が基準値を超え基準値に所定値を加算した値以下であってハンドオーバする必要がないとき、各基地局から送信される信号の受信電界強度を第１受信電界強度とし、通信中の基地局から送信される信号の受信電界強度が基準値以下でハンドオーバする必要があるとき、各基地局から送信される信号の受信電界強度を第２受信電界強度とする。第１受信電界強度と第２受信電界強度とを比較し、第２受信電界強度の方が第１受信電界強度よりも小さい基地局は、ハンドオーバ対象基地局から除かれる。これによって、ハンドオーバ対象として残された基地局の第２受信電界強度は、第１受信電界強度よりも大きいもののみとなり、その中から第２受信電界強度が最大の基地局をハンドオーバ先基地局として選択するので、選択した基地局の受信電界強度は充分に高い水準であり、周辺基地局の測定を行う必要がない受信電界強度である。したがって、受信電界強度が低下しない間は、周辺基地局が送信する信号の受信電界強度の測定もハンドオーバも行う必要がないので、通話時のハンドオーバ回数を抑制し、通話時間への影響も最小限で、かつ通話品質の高い通信を行うことができる。また、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値を超えるとき、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わせずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値以下であるとき、基地局測定禁止中であるか否かを判断し、基地局測定禁止中であれば、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、基地局測定禁止中でなければ、複数の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせて、各基地局から送信される信号の受信電界強度をストア手段にストアさせ、一定時間の基地局測定禁止の状態を設定した後、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせるので、現在通信中の受信レベルが、予め定める基準値を超えている状態であって、ハンドオーバする必要が無いにもかかわらず、過剰な頻度で基地局測定を行い余分な電力を消費して通話時間に対して影響を及ぼさないようにすることができる。
【００１１】
また本発明は、複数の相互に異なる固定位置に設けられた各基地局との通信を行なう無線端末装置において、
複数の基地局から送信される信号の受信電界強度を測定する受信電界強度測定手段と、
測定した受信電界強度と予め定める基準値および基準値に所定値を加算した値とを比較する手段と、
比較手段の出力に応答し、通信中の基地局から送信される信号の受信電界強度が、基準値を超え基準値に所定値を加算した値以下であるとき、各基地局から送信される信号の受信電界強度を第１受信電界強度としてストアし、通信中の基地局から送信される信号の受信電界強度が、基準値以下であるとき、各基地局から送信される信号の受信電界強度を第２受信電界強度としてストアする手段と、
第１受信電界強度よりも第２受信電界強度が小さい基地局を選び、前記選んだ基地局の第２受信電界強度から予め定める補正値を減算して、補正第２受信電界強度を求め、
第１受信電界強度よりも第２受信電界強度が大きい基地局を選び、前記選んだ基地局の第２受信電界強度と、前記求めた補正第２受信電界強度との中から、受信電界強度が最大である基地局を選択する手段と、
通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値を超えるとき、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わせずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値以下であるとき、基地局測定禁止中であるか否かを判断し、基地局測定禁止中であれば、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、基地局測定禁止中でなければ、複数の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせて、各基地局から送信される信号の受信電界強度をストア手段にストアさせ、一定時間の基地局測定禁止の状態を設定した後、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせる手段とを含むことを特徴とする無線端末装置である。
【００１２】
本発明に従えば、第１受信電界強度と第２受信電界強度とを比較し、第２受信電界強度の方が第１受信電界強度よりも小さければ、第２受信電界強度から補正値を減算した値を補正第２受信電界強度として求め、第１受信電界強度よりも第２受信電界強度が大きい基地局の第２受信電界強度と、前記求めた補正第２受信電界強度との中から、最大の受信電界強度を示す基地局をハンドオーバ先基地局として選択する。このように、第２受信電界強度が第１受信電界強度よりも小さい基地局であってもハンドオーバ対象基地局に含めて扱われるので、移動しているＰＨＳ利用者から遠ざかっている基地局であっても、補正第２受信電界強度が高ければハンドオーバ先基地局として選択される。受信電界強度から補正値を減算する補正を行なっても、なお受信電界強度が高ければ、実際の通信においては減算した補正値の分だけ受信電界強度が低下するまでの余裕があり、ハンドオーバしても通信時間を確保することができ、フェージングによる受信電界強度の変動や雑音も生じにくいので、近づきつつあるけれども受信電界強度が低い基地局よりも、ハンドオーバ直後の通話品質の高い通信を行うことができる。また、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値を超えるとき、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わせずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値以下であるとき、基地局測定禁止中であるか否かを判断し、基地局測定禁止中であれば、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、基地局測定禁止中でなければ、複数の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせて、各基地局から送信される信号の受信電界強度をストア手段にストアさせ、一定時間の基地局測定禁止の状態を設定した後、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせるので、現在通信中の受信レベルが、予め定める基準値を超えている状態であって、ハンドオーバする必要が無いにもかかわらず、過剰な頻度で基地局測定を行い余分な電力を消費して通話時間に対して影響を及ぼさないようにすることができる。
【００１３】
また本発明は、複数の相互に異なる固定位置に設けられた各基地局との通信を行なう無線端末装置において、
複数の基地局から送信される信号の受信電界強度を測定する受信電界強度測定手段と、
測定した受信電界強度と予め定める基準値および基準値に所定値を加算した値とを比較する手段と、
比較手段の出力に応答し、通信中の基地局から送信される信号の受信電界強度が、基準値を超え基準値に所定値を加算した値以下であるとき、各基地局から送信される信号の受信電界強度を第１受信電界強度としてストアし、通信中の基地局から送信される信号の受信電界強度が、基準値以下であるとき、各基地局から送信される信号の受信電界強度を第２受信電界強度としてストアする手段と、各基地局ごとに第２受信電界強度から第１受信電界強度を減算して受信電界強度差を求め、
前記求めた受信電界強度差を第２受信電界強度に加算して第３受信電界強度を求め、
前記求めた第３受信電界強度の中から、受信電界強度が最大である基地局を選択する手段と、
通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値を超えるとき、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わせずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値以下であるとき、基地局測定禁止中であるか否かを判断し、基地局測定禁止中であれば、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、基地局測定禁止中でなければ、複数の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせて、各基地局から送信される信号の受信電界強度をストア手段にストアさせ、一定時間の基地局測定禁止の状態を設定した後、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせる手段とを含むことを特徴とする無線端末装置である。
【００１４】
本発明に従えば、第１受信電界強度と第２受信電界強度とを比較し、第２受信電界強度と第１受信電界強度との受信電界強度差を求め、前記求めた受信電界強度差を第２受信電界強度に加算したものを第３受信電界強度として、第３受信電界強度の中からハンドオーバ先基地局を選択する。ハンドオーバ先基地局を選択してから、実際に通信を開始するまでには時間のずれがあるので、ＰＨＳ利用者が近づきつつある基地局をハンドオーバ先に選択した場合には、基地局決定から通信開始までの間に受信電界強度が増加し、逆にＰＨＳ利用者が遠ざかりつつある基地局をハンドオーバ先に選択した場合には、基地局決定から通信開始までの間に受信電界強度が減少することになる。また、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値を超えるとき、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わせずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値以下であるとき、基地局測定禁止中であるか否かを判断し、基地局測定禁止中であれば、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、基地局測定禁止中でなければ、複数の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせて、各基地局から送信される信号の受信電界強度をストア手段にストアさせ、一定時間の基地局測定禁止の状態を設定した後、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせるので、現在通信中の受信レベルが、予め定める基準値を超えている状態であって、ハンドオーバする必要が無いにもかかわらず、過剰な頻度で基地局測定を行い余分な電力を消費して通話時間に対して影響を及ぼさないようにすることができる。
【００１５】
第２受信電界強度と第１受信電界強度との受信電界強度差を、第２受信電界強度に加算した値を第３受信電界強度として、その中からハンドオーバ先基地局を選択することによって、基地局を選択してから実際に通信が開始されるまでの間の受信電界強度の増減を想定した基地局の選択をすることができる。したがって、通信を開始した時点において受信電界強度が高い最適のハンドオーバ先基地局を選択することができるので、通話時のハンドオーバ回数を抑制し、通話時間への影響も最小限で、かつ通話品質の高い通信を行うことができる。
【００１６】
【発明の実施の形態】
図１は、本発明の実施の一形態であるＰＨＳ１の概略的な構成を示すブロック図である。ＰＨＳ１は、筐体２と、筐体２から外方に延びて電磁波の送受信を行うアンテナ部３と、筐体２内に納められ、アンテナ部３に接続されて送受信した信号を復調および変調する無線部４と、アナログ信号とデジタル信号とを相互変換するアナログ／デジタル変換器５と、帯域制限等に関する音の制御を行う音声処理部６と、音声の入出力を行うマイクロホン７およびスピーカ８と、たとえば中央演算処理装置によって実現され、無線部４、アナログ／デジタル変換器５、音声処理部６、マイクロホン７、スピーカ８の動作制御と入力情報についての処理を行う制御部９と、制御部９の動作プログラムをストアする第１メモリ（以後、ＲＯＭと呼ぶ）１０と、受信した各基地局に関する情報をストアする第２メモリ（以後、ＲＡＭと呼ぶ）１１とを含む。
【００１７】
制御部９は、ＲＯＭ１０から読み出したプログラムにしたがって動作し、複数の周辺基地局から送信される信号の電界強度の測定を行う。制御部９からの信号は、アナログ／デジタル変換器５によってアナログ信号に変換され、無線部４において変調処理されて、その後周波数変換してアンテナ部３から送信される。
【００１８】
周辺基地局からの受信電界強度を測定した結果得られる基地局情報である基地局識別子（以後、ＣＳＩＤと呼ぶ）、受信電界強度およびスロット情報は、アンテナ部３によって受信され、受信信号は無線部４によって周波数変換された後復調処理されて、アナログ／デジタル変換器５によって制御部９で処理可能なようにデジタル信号に変換されて制御部９に送られる。基地局情報は、制御部９において、データとして演算処理されたり、ＲＡＭ１１にストアされる。ＲＡＭ１１にストアされる基地局情報は、必要に応じて読み出され、制御部９において演算処理される。演算結果に応答し、制御部９においてハンドオーバ先基地局を選択し、ハンドオーバを実行する。
【００１９】
本発明の実施の一形態におけるハンドオーバ先基地局の選択方法について説明する。本発明の実施の一形態においては、受信レベルが時系列的に小さくなる基地局を選択対象から除き、受信レベルが時系列的に大きくなる基地局の中から、最大受信レベルをもつ基地局を選ぶ。
図２は、ＰＨＳの移動に伴うハンドオーバについての概念を示す図である。図２中の円は、それぞれ基地局１〜５が、移動局であるＰＨＳと良好な通信をすることのできる範囲であるセルを表しており、円の中心に基地局が存在する。したがって、円周上の位置はハンドオーバを行なう必要のある地点を表す。図２中の矢符１２は、ＰＨＳが移動する方向を示しており、記号ａ，ｂ，ｃ，ｄは、それぞれＰＨＳの移動途上において基地局情報の測定を行ない、測定結果を受信した位置を表す。
【００２０】
表１に、図２のａ，ｂ，ｃ，ｄの各位置で、基地局１〜５の基地局情報測定を行った結果得られた受信電界強度を示す。表１中の受信電界強度を示す数値の単位は［ｄＢμＶ］である。なお、以後の説明および後述の各フローチャートにおいては、受信電界強度を受信レベルと呼ぶ。
【００２１】
基地局５との間で通信中のＰＨＳが、矢符１２の示す方向に移動したとする。ａ地点までの移動では、ａ地点における基地局５からの受信レベルである４０は、基準値であるハンドオーバ保持レベル３０に所定値１０を加算した４０以上であるため、周辺基地局の測定を行なわず基地局５との間で通信を継続することができる。したがって、ＰＨＳ１がａ地点まで移動する間は、余分な電力を消費することなく充分な通話時間を確保することができる。この場合、先行技術では、受信レベルの最も高い基地局４にハンドオーバすることになり、ハンドオーバする必要がないときにハンドオーバするための電力を不要に消費することになる。
【００２２】
ＰＨＳが、さらに移動してａ−ｂ間に到達すると、受信レベルが基準値以上であるけれども、所定値を加算した値４０未満になるので、フェージング等の影響を受けやすくハンドオーバを行う可能性が高くなる。したがって、周辺基地局情報の測定を行ない、受信した基地局情報である各基地局ごとのＣＳＩＤおよび第１受信レベルを前回受信基地局情報としてＲＡＭ１１にストアする。
【００２３】
ＰＨＳが、さらに移動してｂ地点に達すると、ｂ地点は基地局５のセルを表わす円の円周上に位置するので、基地局５と良好な通信を行うことが困難となり、ハンドオーバ対象基地局情報の測定が開始される。ｂ地点における基地局情報測定の結果、今回受信基地局情報として各基地局ごとにＣＳＩＤおよび第２受信レベルが得られる。今回受信基地局情報の中では、基地局４の第２受信レベルが５５と最も高いけれども、第１受信レベルである６０に比べて減少しているので、基地局４はｂ地点におけるハンドオーバ対象基地局から除かれる。なお、現在通信中の基地局５も、第１受信レベルである４０に比べて、第２受信レベルは３０と減少しているので、ハンドオーバ対象基地局から除かれる。この処理によって、移動しているＰＨＳ利用者から遠ざかっている基地局のように、ハンドオーバ直後の受信レベルは高くても、その後の受信レベルが減少して再度ハンドオーバ処理が必要となる基地局を選択することがなくなる。
【００２４】
残る基地局１〜３は、いずれも第１受信レベルよりも第２受信レベルが大きいので、ハンドオーバ対象基地局とされる。基地局１〜３の中では、基地局３の第２受信レベルが４０と最も大きいので、基地局３がｂ地点におけるハンドオーバ先基地局として選択される。
【００２５】
このときの基地局３の第２受信レベルである４０は、基準値に所定値を加算した値４０以上であり、受信レベルが充分高い水準なので周辺基地局情報の測定を行う必要がない。したがって、受信レベルが減少しない間は、前述のように、周辺基地局情報の測定を行わず余分な電力を必要としないので、通話を継続することができ、充分な通話時間を確保することができる。基地局３をハンドオーバ先基地局として選択した後、今回受信基地局情報を前回受信基地局情報としてＲＡＭ１１にストアし、ＰＨＳの移動にともなう次のハンドオーバ対象基地局情報の測定に備える。ＰＨＳが、ｂからさらにｃ，ｄへと移動した場合も前記と同じ処理を行ない、ハンドオーバ先基地局を選択する。
【００２６】
以上の処理によって、通話時間への影響を最小限に抑えて、通話時のハンドオーバ回数を少なくし、かつ通話品質の高い通話を実現することができる。
【００２７】
【表１】

【００２８】
図３は、本発明の実施の一形態であるＰＨＳ１の制御部９のハンドオーバ処理動作を説明するフローチャートである。なお、フローチャートにおいては、測定および測定検索の両方の用語を使用しているが、いずれも同じ意味で使用しており、以後の説明では測定で統一する。
【００２９】
ステップａ１では、通信を開始する時に前回の通信時において受信した基地局情報等の各種初期化を行い通信状態とする。ステップａ２では、受信レベルを測定する受信レベル測定手段によって、現在通信中の基地局の受信レベル測定を開始する。ステップａ３では、現在通信中の受信信号について繰返し受信レベルの測定を行う。ステップａ４では、受信レベルの測定が所定回数できたか否かを判断する。受信レベルを所定回数測定することができていなければ、ステップａ３の受信レベルの測定に戻る。受信レベルを所定回数測定することができていれば、ステップａ５に進み、受信レベルの平均値を算出する。ステップａ６では、測定した受信レベルと予め定める基準値とを比較する手段によって、ハンドオーバ起動条件が成立するか否かが判断される。すなわち、ステップａ５において算出された受信レベルの平均値が一定時間、予め定める基準値以下であるか否かが判断される。ここで予め定める基準値は、ハンドオーバ保持レベルと呼ぶハンドオーバを必要とする臨界の受信レベルである。
【００３０】
ステップａ６において、現在通信中の受信レベルの平均値が、一定時間、予め定める基準値を超えていると判断されると、ハンドオーバを起動させることなく、ステップａ７に進む。ステップａ７では、基地局測定起動条件が成立するか否かが判断される。すなわち、現在通信中の受信レベルが、前記基準値に所定値を加算した値未満であるか否かを判断する。ここで、所定値は、運用に基づいて決定される値である。現在通信中の受信レベルが、前記基準値に所定値を加算した値未満であるとき、ステップａ８において、基地局測定禁止タイマが作動中であるか否かを判断し、基地局測定禁止タイマが作動中のときは、周辺基地局情報の測定は行わず、ステップａ３に戻る。基地局測定禁止タイマが作動中でなければ、ステップａ９において、複数の周辺基地局について、各基地局が送信する基地局情報であるＣＳＩＤおよび受信レベルなどの測定を行う。周辺基地局情報測定中は、受信した基地局情報をＲＡＭ１１にストアする。
【００３１】
ステップａ７において、現在通信中の受信レベルが、前記基準値に所定値を加算した値以上であるときは、ステップａ３に戻る。すなわち現在通信中の受信レベルが高く、通話品質が良好であるときは、周辺基地局情報の測定を行わない。したがって、余分な電力を消費することがない。また、ステップａ９では、各基地局ごとの測定終了後、測定中に同一の基地局情報を複数回受信した場合、受信レベルは平均値を求める。ステップａ１０では、受信した基地局情報である各基地局ごとのＣＳＩＤおよび受信レベルの平均値を第１受信レベルとし、ストア手段であるＲＡＭ１１に前回受信基地局情報としてストアする。
【００３２】
ステップａ１１では、一定時間（Ｔ秒間）基地局測定禁止の状態を設定する。Ｔ秒間は、運用に基づいて決定される値である。この一定時間基地局測定禁止状態を設定する目的は、現在通信中の受信レベルが、予め定める基準値を超えている状態であって、ハンドオーバする必要が無いにもかかわらず、過剰な頻度で基地局測定を行い余分な電力を消費して通話時間に対して影響を及ぼさないようにすることにある。ステップａ１１において、Ｔ秒間の基地局測定禁止時間を設定した後、ステップａ３の通信中基地局の受信レベル測定に戻る。
【００３３】
前記ステップａ６において、現在通信中の受信レベルの平均値が、一定時間、基準値以下であると判断されるとハンドオーバ起動条件が成立し、ステップａ１２に進む。ステップａ１２では、先のステップａ９において周辺の基地局測定を行なったのと同じ条件でハンドオーバ対象基地局の測定を行なう。測定中は、ハンドオーバ対象基地局の情報であるＣＳＩＤおよび受信レベルを第２受信レベルとし、ストア手段であるＲＡＭ１１に今回受信基地局情報としてストアする。
【００３４】
ハンドオーバ対象基地局の測定が終了すると、ステップａ１３に進む。ステップａ１３では、今回受信基地局情報としてＲＡＭ１１にストアした各基地局ごとのＣＳＩＤおよび第２受信レベルと、前記ステップａ１０において前回受信基地局情報としてＲＡＭ１１にストアした各基地局ごとのＣＳＩＤおよび第１受信レベルとを、制御部９において比較する。比較の結果、今回受信基地局情報と前回受信基地局情報とにおいて、ＣＳＩＤが一致する基地局情報があれば、それぞれ一致する基地局ごとに第２受信レベルと第１受信レベルとの受信レベル差を演算する。また、比較の結果、今回受信基地局情報と前回受信基地局情報とにおいて、ＣＳＩＤが一致する基地局情報が無ければ、今回受信基地局情報を前回受信基地局情報としてＲＡＭ１１にストアする。
【００３５】
ステップａ１４では、第１受信レベルよりも第２受信レベルが小さい、すなわち第１受信レベルに比べて第２受信レベルが減少している基地局をハンドオーバ対象基地局から除く処理を行なう。ステップａ１５では、第１受信レベルよりも第２受信レベルが大きい基地局の中から、第２受信レベルが最大である基地局をハンドオーバ先の基地局として選択する。
【００３６】
ステップａ１６では、ハンドオーバ先基地局を選択した後、ハンドオーバ対象基地局測定の結果得られた今回受信基地局情報を、前回受信基地局情報としてＲＡＭ１１にストアする。ステップａ１７では、ステップａ１５において選択したハンドオーバ先基地局に対して、ハンドオーバ処理を実施する。ステップａ１８では、ハンドオーバ処理が成功したか否かを判断し、ハンドオーバ先基地局から通信チャネルの通知を得てハンドオーバ処理が成功した場合は、ステップａ１９に進み、ハンドオーバ先基地局の前回受信基地局情報を初期化し、ハンドオーバに成功した新たな基地局と通信状態となる。ステップａ１９において、新たな基地局と通信状態になると、現在通信中の基地局の受信レベル測定を行うステップａ３に戻り、以降のステップに進む。
【００３７】
ステップａ１８において、ハンドオーバ処理が失敗した場合は、ステップａ２０に進み、ハンドオーバ処理を開始する前に通信していた基地局に戻る（切戻り）処理をして、ステップａ２１で通信復活を行なう。切戻り処理に成功すれば、ハンドオーバ処理を開始する前に通信していた基地局との通信が復活し、現在通信中の基地局の受信レベル測定を行うステップａ３に戻り、以降のステップに進む。切戻り処理に失敗すれば、ハンドオーバ先基地局およびハンドオーバ処理を開始する前に通信していた基地局のいずれの基地局とも通信を行うことができず、通信は終了する。
【００３８】
本発明の他の実施の形態として、第２受信レベルが第１受信レベルよりも小さい場合でも、ハンドオーバ先基地局として選局対象とするように構成してもよい。本発明の他の実施の形態におけるハンドオーバ先基地局の選択方法について説明する。
【００３９】
ＰＨＳ利用者が移動してｂ地点に到達し、ｂ地点における基地局情報を測定し、測定の結果、今回受信基地局情報として各基地局ごとにＣＳＩＤおよび第２受信レベルを得るところまでは、前記実施の一形態と同じであるため、説明は省略する。今回受信基地局情報の中から、第１受信レベルよりも第２受信レベルが小さい基地局である基地局４および５を選ぶ。基地局４および５の第２受信レベルである５５および３０から、予め定める補正値１０を減算して、補正第２受信レベル４５および２０をそれぞれ求める。他の実施の形態では、第１受信レベルよりも第２受信レベルが小さい基地局であっても、補正第２受信レベルを求め、補正第２受信レベルをハンドオーバ先基地局の判別に用いる数値として、ハンドオーバ対象基地局に含めて扱われる。第１受信レベルよりも第２受信レベルが大きい基地局１〜３の第２受信レベルと、前記求めた基地局４および５の補正第２受信レベルとの中から、受信レベルが４５と最も大きい基地局４をハンドオーバ先基地局として選択する。
【００４０】
以上のように、本発明の他の実施の形態では、前記ｂ地点においてハンドオーバ先基地局として基地局４が選ばれる。基地局４は、第１受信レベルよりも第２受信レベルが小さく、ｂ地点においては移動するＰＨＳ利用者からは遠ざかりつつあるけれども、補正値を減算する補正を行ってもなお補正第２受信レベルは４５と高い。基地局４の実際の受信レベルは、第２受信レベルである５５であることから、実際の通信においては減算した補正値の分だけ受信レベルが減少するまでの余裕があり、ハンドオーバしても通信時間を確保することができる。また、受信レベルが高いので、フェージングによる雑音も生じにくく、近づきつつあるけれども受信レベルが低い基地局よりも、ハンドオーバ直後の通話品質の高い通信を行うことができる。
【００４１】
図４は、本発明の他の実施の形態であるＰＨＳの制御部のハンドオーバ処理動作を説明するフローチャートである。他の実施の形態のフローチャートは、実施の一形態と類似し、ステップｂ１４とステップａ１４とが異なる以外は全く同一であるので重複する説明を省略する。
【００４２】
本実施の形態のステップｂ１４では、ハンドオーバ先基地局情報測定の結果得られた基地局情報において、基地局ごとに第２受信レベルと第１受信レベルとを比較し、第２受信レベルが第１受信レベルよりも小さい基地局をハンドオーバ対象基地局から除くのではなく、第２受信レベルから補正値を減算した値を補正第２受信レベルとしてハンドオーバ先対象基地局に含める。ハンドオーバ先基地局の選択は、実施の一形態と同様にステップｂ１５において、第１受信レベルよりも大きい基地局の第２受信レベルと前記求めた補正第２受信レベルとの中から、受信レベルが最大の基地局を選択する。
【００４３】
本発明のさらに他の実施の形態として、ハンドオーバ先基地局の受信レベルの増減を予測して選局対象とするように構成してもよい。本発明のさらに他の実施の形態におけるハンドオーバ先基地局の選択方法について説明する。
【００４４】
ＰＨＳ利用者が移動してｂ地点に到達し、ｂ地点における基地局情報を測定し、測定の結果、今回受信基地局情報として各基地局ごとにＣＳＩＤおよび第２受信レベルを得るところまでは、前記実施の一形態と同じであるため、説明は省略する。
【００４５】
各基地局ごとに、第２受信レベルから第１受信レベルを減算して受信レベル差を求め、次に、前記求めた受信レベル差を第２受信レベルに加算して第３受信レベルを求める。たとえば、第１受信レベルよりも第２受信レベルが大きい基地局２では、第２受信レベル３５から第１受信レベル２０を減算して、受信レベル差１５を求め、次に、第２受信レベル３５に受信レベル差１５を加算して、第３受信レベル５０を求める。第１受信レベルよりも第２受信レベルが小さい基地局５では、第２受信レベル３０から第１受信レベル４０を減算して、受信レベル差マイナス１０を求め、次に、第２受信レベル３０に受信レベル差マイナス１０を加算して、第３受信レベル２０を求める。同様に他の基地局についても第３受信レベルを求め、求めた第３受信レベルの中から、受信レベルが最も大きい基地局３をハンドオーバ先基地局として選択する。
【００４６】
ハンドオーバ処理においては、ハンドオーバ先基地局を選択してから、実際に通信が開始するまでには時間のずれがある。したがって、ＰＨＳ利用者が近づきつつある基地局をハンドオーバ先に決定した場合には、基地局選択から通信開始までの間に受信レベルが増加することになる。逆に、ＰＨＳ利用者が遠ざかりつつある基地局をハンドオーバ先に選択した場合には、基地局選択から通信開始までの間に受信レベルが減少することになる。
【００４７】
本発明のさらに他の実施形態のように、受信レベル差を加算した値を第３受信レベルとし、第３受信レベルの中からハンドオーバ先基地局を選択することによって、基地局を選択してから実際に通信が開始されるまでの間の受信レベルの増減を想定した基地局の選択をすることができる。したがって、通信を開始した時点において受信レベルが高い最適のハンドオーバ先基地局を選択することができるので、通話時のハンドオーバ回数を抑制し、通話時間への影響も最小限で、かつ通話品質の高い通信を行うことができる。
【００４８】
図５は、本発明のさらに他の実施の形態であるＰＨＳの制御部のハンドオーバ処理動作を説明するフローチャートである。さらに他の実施の形態のフローチャートは、実施の一形態と類似し、ステップｃ１４とステップａ１４とが異なる以外は全く同一であるので重複する説明を省略する。
【００４９】
本実施の形態のステップｃ１４では、ハンドオーバ対象基地局情報測定の結果得られた基地局情報において、基地局ごとに第２受信レベルと第１受信レベルとを比較し、第２受信レベルから第１受信レベルを減算して得られる受信レベル差を、第２受信レベルに加算した値を第３受信レベルとする。ハンドオーバ先基地局の選択は、実施の一形態と同様にステップｃ１５において、第３受信レベルの中から、受信レベルが最大の基地局を選択する。
【００５０】
以上述べたように、本発明のそれぞれの実施の形態では、無線端末装置としてＰＨＳが用いられるけれども、これに限定されることはなく、ＰＨＳに比べてセルの広い携帯電話装置（Personal Digital Cellular）およびその他の無線通信を行なう装置、たとえばタクシー無線装置などであってもよい。
【００５１】
【発明の効果】
以上のように本発明によれば、通信中の基地局から送信される信号の受信電界強度と予め定める基準値および基準値に所定値を加算した値とを比較する。比較結果の出力に応答し、通信中の基地局から送信される信号の受信電界強度が基準値に所定値を加算した値を超えるとき、各基地局から送信される受信電界強度を測定することなく通信中の基地局との通信を継続し、通信中の基地局から送信される信号の受信電界強度が基準値を超え基準値に所定値を加算した値以下であってハンドオーバする必要がないとき、各基地局から送信される信号の受信電界強度を第１受信電界強度とし、通信中の基地局から送信される信号の受信電界強度が基準値以下でハンドオーバする必要があるとき、各基地局から送信される信号の受信電界強度を第２受信電界強度とする。第１受信電界強度と第２受信電界強度とを比較し、第２受信電界強度の方が第１受信電界強度よりも小さい基地局は、ハンドオーバ対象基地局から除かれる。これによって、ハンドオーバ対象として残された基地局の第２受信電界強度は、第１受信電界強度よりも大きいもののみとなり、その中から第２受信電界強度が最大の基地局をハンドオーバ先基地局として選択するので、選択した基地局の受信電界強度は充分に高い水準であり、周辺基地局の測定を行う必要がない受信電界強度である。したがって、受信電界強度が低下しない間は、周辺基地局が送信する信号の受信電界強度の測定もハンドオーバも行う必要がないので、通話時のハンドオーバ回数を抑制し、通話時間への影響も最小限で、かつ通話品質の高い通信を行うことができる。
また、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値を超えるとき、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わせずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、通信中の基地局から送信される信号の受信電界強度が、予め定める基準値を超え、前記基準値に所定値を加算した値以下であるとき、基地局測定禁止中であるか否かを判断し、基地局測定禁止中であれば、複数の基地局のうち通信中の基地局を除く残余の基地局から送信される信号の受信電界強度の測定は行わずに、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせ、基地局測定禁止中でなければ、複数の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせて、各基地局から送信される信号の受信電界強度をストア手段にストアさせ、一定時間の基地局測定禁止の状態を設定した後、通信中の基地局から送信される信号の受信電界強度の測定を受信電界強度測定手段に行わせるので、現在通信中の受信レベルが、予め定める基準値を超えている状態であって、ハンドオーバする必要が無いにもかかわらず、過剰な頻度で基地局測定を行い余分な電力を消費して通話時間に対して影響を及ぼさないようにすることができる。
【００５２】
また本発明によれば、第１受信電界強度と第２受信電界強度とを比較し、第２受信電界強度の方が第１受信電界強度よりも小さければ、第２受信電界強度から補正値を減算した値を補正第２受信電界強度として求め、前記選んだ基地局の第２受信電界強度と、前記求めた補正第２受信電界強度との中から、最大の受信電界強度を示す基地局をハンドオーバ先基地局として選択する。このように、前記第２受信電界強度が第１受信電界強度よりも小さい基地局であってもハンドオーバ対象基地局に含めて扱われるので、移動しているＰＨＳ利用者から遠ざかっている基地局であっても、補正第２受信電界強度が高ければハンドオーバ先基地局として選択される。受信電界強度から補正値を減算する補正を行なっても、なお受信電界強度が高ければ、実際の通信においては減算した所定値の分だけ受信電界強度が低下するまでの余裕があり、ハンドオーバしても通信時間を確保することができ、フェージングによる雑音も生じにくいので、近づきつつあるけれども受信電界強度が低い基地局よりも、ハンドオーバ直後の通話品質の高い通信を行うことができる。
【００５３】
また本発明によれば、第１受信電界強度と第２受信電界強度とを比較し、第２受信電界強度から第１受信電界強度を減算して得られる受信電界強度差を求め、前記求めた受信電界強度差を第２受信電界強度に加算したものを第３受信電界強度として、第３受信電界強度の中からハンドオーバ先基地局を選択する。ハンドオーバ先基地局を選択してから、実際に通信を開始するまでには時間のずれがあるので、ＰＨＳ利用者が近づきつつある基地局をハンドオーバ先に選択した場合には、基地局選択から通信開始までの間に受信電界強度が増加し、逆にＰＨＳ利用者が遠ざかりつつある基地局をハンドオーバ先に選択した場合には、基地局選択から通信開始までの間に受信電界強度が減少することになる。
【００５４】
第２受信電界強度から第１受信電界強度を減算して得られる受信電界強度差を、第２受信電界強度に加算した値を第３受信電界強度として、その中からハンドオーバ先基地局を選択することによって、基地局を選択してから実際に通信が開始されるまでの間の受信電界強度の増減を想定した基地局の選択をすることができる。したがって、通信を開始した時点において受信電界強度が高い最適のハンドオーバ先基地局を選択することができるので、通話時のハンドオーバ回数を抑制し、通話時間への影響も最小限で、かつ通話品質の高い通信を行うことができる。
【図面の簡単な説明】
【図１】本発明の実施の一形態であるＰＨＳ１の概略的な構成を示すブロック図である。
【図２】ＰＨＳの移動にともなうハンドオーバについての概念を示す図である。
【図３】本発明の実施の一形態であるＰＨＳ１の制御部９のハンドオーバ処理動作を説明するフローチャートである。
【図４】本発明の他の実施の形態であるＰＨＳの制御部のハンドオーバ処理動作を説明するフローチャートである。
【図５】本発明のさらに他の実施の形態であるＰＨＳの制御部のハンドオーバ処理動作を説明するフローチャートである。
【符号の説明】
１ＰＨＳ
２筐体
３アンテナ部
４無線部
５アナログ／デジタル変換器
６音声処理部
７マイクロホン
８スピーカ
９制御部
１０ＲＯＭ
１１ＲＡＭ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wireless terminal device that forms a wireless communication network in combination with a base station.
[0002]
[Prior art]
Since the personal handyphone system (hereinafter referred to as PHS), which is a wireless terminal device, is a small zone system in which the electromagnetic wave reach of the base station is narrow, the range that can communicate with one base station is about 100 to 500 m in radius. small. Therefore, when moving during PHS communication, a process of taking over communication from one base station to an adjacent base station (hereinafter referred to as handover) is performed.
[0003]
For handover, when a handover is requested from the base station to the PHS which is the mobile station, the received electric field strength of the signal being communicated by the PHS is measured, and the received electric field strength specified by the base station (re-occurring) There are two types in which handover processing is performed by determining that the call-type handover holding level is below the call-type handover holding level). In either case, when the handover is started, the received field strength of the neighboring base stations is measured, and the base station having the highest received field strength is selected from the received base stations.
[0004]
In the handover process defined in the second generation cordless telephone system standard RCRSTD-28, the base station is selected based on the judgment that the received field strength is the highest among the base stations received as described above, and the handover is performed. Do. If the PHS user is moving at the speed of stopping and walking, there is no particular communication problem even if the base station is selected based on the judgment that the received electric field strength is the highest. However, when moving at a high speed exceeding the walking speed, for example, by car or train, the base station selected based on the judgment that the received electric field strength is the highest is the direction opposite to the traveling direction of the PHS user. In this case, the received electric field strength of the base station selected as the handover destination rapidly decreases with the movement of the PHS user. Therefore, even if the handover cannot be performed or the handover can be performed, it is immediately transferred to another base station. There was a problem of having to hand over.
[0005]
Japanese Patent Laid-Open No. 8-154264 is disclosed as a prior art for solving the problem of setting such a handover destination base station selection criterion to only the highest received electric field strength. In this prior art, the received electric field strength transmitted from neighboring base stations is stored, compared with the received electric field strength after a certain time, and when a base station whose difference in received electric field strength exceeds a predetermined value is found. Selects the base station as a handover destination, and when any base station has a difference in received electric field strength that is a predetermined value or less, a change in the received electric field strength is obtained in time series for each base station, The base station with the largest amount of time-series change in received electric field strength is selected as the handover destination.
[0006]
[Problems to be solved by the invention]
This prior art handover process has the following problems. Stores the received field strength of neighboring base stations, finds the received field strength difference from the received field strength after a certain period of time, and finds a base station whose received field strength difference exceeds a predetermined value. Since the handover is performed even when the communication state is good, unnecessary handover may be performed, and the number of handovers is increased unnecessarily. In addition, when the difference in received field strength between neighboring base stations is less than or equal to a predetermined value, the handover destination base station is based on the time-series change in received field strength regardless of the absolute value of the received field strength. Therefore, the received electric field strength of the selected base station of the handover destination may be lower than the received electric field strength of the currently communicating base station.
[0007]
PHS is often used while moving, and when the received electric field strength of the base station selected as the handover destination is low, the received electric field strength of electromagnetic waves varies with time depending on the surrounding environment of the PHS destination, so-called fading. As a result, noise may be generated and the call quality may be degraded. If the call quality deteriorates, a handover request is issued from the base station, and the number of handovers increases. Further, the selection of the handover destination base station based on the time series change amount of the received electric field strength means that the handover destination base station is selected by predicting the movement destination of the PHS user. If the PHS user's movement destination prediction does not match the prediction based on the time-series variation of the received electric field strength, the received electric field strength is lower than the prediction, so the handover is performed again. This must be done and does not necessarily reduce the number of handovers. Furthermore, since the measurement of the received electric field strength of the neighboring base stations is repeated every predetermined time regardless of the call state during the current communication, for example, the received electric field strength is high and the call quality is good when the PHS user is stopped. In this case, useless operation is performed and extra power is consumed, which has the effect of reducing the call time by using up the battery.
[0008]
The present invention provides a wireless terminal device that has little influence on call time and call quality and can be handed over to an optimal base station during movement.
[0009]
[Means for Solving the Problems]
The present invention provides a wireless terminal device that performs communication with a plurality of base stations provided at a plurality of mutually different fixed positions.
Received field strength measuring means for measuring received field strength of signals transmitted from a plurality of base stations;
Means for comparing the measured received field strength with a predetermined reference value and a value obtained by adding a predetermined value to the reference value;
A signal transmitted from each base station when the received electric field strength of the signal transmitted from the communicating base station is less than a value obtained by adding a predetermined value to the reference value in response to the output of the comparison means Is stored as the first received electric field strength, and when the received electric field strength of the signal transmitted from the communicating base station is equal to or lower than the reference value, the received electric field strength of the signal transmitted from each base station is Means for storing as a second received field strength;
A base station having a second received electric field strength greater than the first received electric field strength is selected, and among the base stations having a second received electric field strength greater than the first received electric field strength, the base having the maximum second received electric field strength. Means for selecting a station;
The received electric field strength of the signal transmitted from the communicating base station is Predetermined Standard value Without exceeding the value obtained by adding a predetermined value to the reference value without measuring the received field strength of signals transmitted from the remaining base stations excluding the communicating base station among the plurality of base stations. The reception electric field strength measurement unit performs measurement of the reception electric field strength of the signal transmitted from the communicating base station, and the reception electric field strength of the signal transmitted from the communicating base station exceeds a predetermined reference value. When it is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether or not base station measurement is prohibited, and if base station measurement is prohibited, a base station in communication among a plurality of base stations is determined. Measurement of the received electric field strength of the signal transmitted from the communicating base station is performed by the received electric field strength measuring means without measuring the received electric field strength of the signal transmitted from the remaining base station. If not prohibited, the signal transmitted from multiple base stations The measurement of the signal field strength to perform the reception field strength measuring unit, is stored in the store means the reception field strength of the signal transmitted from each base station, Fixed time After the base station measurement prohibition state is set, the reception field strength measurement unit measures the reception field strength of the signal transmitted from the communicating base station. A wireless terminal device.
[0010]
According to the present invention, the received electric field strength of the signal transmitted from the communicating base station is compared with a predetermined reference value and a value obtained by adding a predetermined value to the reference value. As the reference value, for example, a critical received electric field strength that requires handover is set, and for example, 10 dBμV is set as the predetermined value. Measure the received field strength transmitted from each base station when the received field strength of the signal transmitted from the communicating base station exceeds the reference value plus a predetermined value in response to the output of the comparison result. Without continuing to communicate with the communicating base station, the received electric field strength of the signal transmitted from the communicating base station exceeds the reference value and is equal to or less than the value obtained by adding a predetermined value to the reference value, and there is no need for handover. When the received field strength of the signal transmitted from each base station is the first received field strength and the received field strength of the signal transmitted from the communicating base station needs to be handed over at a reference value or less, The received field strength of the signal transmitted from the station is set as the second received field strength. The first received electric field strength is compared with the second received electric field strength, and the base station whose second received electric field strength is smaller than the first received electric field strength is excluded from the handover target base stations. As a result, the second received electric field strength of the base station left as a handover target is only larger than the first received electric field strength, and the base station having the maximum second received electric field strength is selected as the handover destination base station. Since the selection is made, the received electric field strength of the selected base station is at a sufficiently high level, and the received electric field strength is not required to measure the neighboring base stations. Therefore, as long as the received field strength does not decrease, there is no need to measure the received field strength of signals transmitted from neighboring base stations and perform handover, so the number of handovers during a call is suppressed and the impact on the talk time is minimized. In addition, communication with high call quality can be performed. In addition, the received electric field strength of the signal transmitted from the communicating base station is Predetermined Standard value Without exceeding the value obtained by adding a predetermined value to the reference value without measuring the received field strength of signals transmitted from the remaining base stations excluding the communicating base station among the plurality of base stations. The reception electric field strength measurement unit performs measurement of the reception electric field strength of the signal transmitted from the communicating base station, and the reception electric field strength of the signal transmitted from the communicating base station exceeds a predetermined reference value. When it is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether or not base station measurement is prohibited, and if base station measurement is prohibited, a base station in communication among a plurality of base stations is determined. Measurement of the received electric field strength of the signal transmitted from the communicating base station is performed by the received electric field strength measuring means without measuring the received electric field strength of the signal transmitted from the remaining base station. If not prohibited, the signal transmitted from multiple base stations The measurement of the signal field strength to perform the reception field strength measuring unit, is stored in the store means the reception field strength of the signal transmitted from each base station, Fixed time Since the base station measurement prohibition state is set, the reception field strength measurement unit measures the reception field strength of the signal transmitted from the communicating base station. Even if the reception level currently being communicated exceeds a predetermined reference value and there is no need to perform handover, the base station is measured at an excessive frequency and consumes extra power to talk time. It can be made not to affect.
[0011]
Further, the present invention provides a wireless terminal device that performs communication with a plurality of base stations provided at different fixed positions,
Received field strength measuring means for measuring received field strength of signals transmitted from a plurality of base stations;
Means for comparing the measured received field strength with a predetermined reference value and a value obtained by adding a predetermined value to the reference value;
A signal transmitted from each base station when the received electric field strength of the signal transmitted from the communicating base station is less than a value obtained by adding a predetermined value to the reference value in response to the output of the comparison means Is stored as the first received electric field strength, and when the received electric field strength of the signal transmitted from the communicating base station is equal to or lower than the reference value, the received electric field strength of the signal transmitted from each base station is Means for storing as a second received field strength;
Selecting a base station having a second received electric field strength smaller than the first received electric field strength, subtracting a predetermined correction value from the second received electric field strength of the selected base station to obtain a corrected second received electric field strength;
A base station having a second received field strength greater than the first received field strength is selected, and the received field strength is selected from the second received field strength of the selected base station and the calculated corrected second received field strength. Means to select the base station that is the largest,
The received electric field strength of the signal transmitted from the communicating base station is Predetermined Standard value Without exceeding the value obtained by adding a predetermined value to the reference value without measuring the received field strength of signals transmitted from the remaining base stations excluding the communicating base station among the plurality of base stations. The reception electric field strength measurement unit performs measurement of the reception electric field strength of the signal transmitted from the communicating base station, and the reception electric field strength of the signal transmitted from the communicating base station exceeds a predetermined reference value. When it is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether or not base station measurement is prohibited, and if base station measurement is prohibited, a base station in communication among a plurality of base stations is determined. Measurement of the received electric field strength of the signal transmitted from the communicating base station is performed by the received electric field strength measuring means without measuring the received electric field strength of the signal transmitted from the remaining base station. If not prohibited, the signal transmitted from multiple base stations The measurement of the signal field strength to perform the reception field strength measuring unit, is stored in the store means the reception field strength of the signal transmitted from each base station, Fixed time After the base station measurement prohibition state is set, the reception field strength measurement unit measures the reception field strength of the signal transmitted from the communicating base station. A wireless terminal device.
[0012]
According to the present invention, the first received electric field strength is compared with the second received electric field strength, and if the second received electric field strength is smaller than the first received electric field strength, the correction value is subtracted from the second received electric field strength. The corrected second received electric field strength is obtained, and the second received electric field strength of the base station having the second received electric field strength larger than the first received electric field strength, and the obtained corrected second received electric field strength, A base station showing the maximum received electric field strength is selected as a handover destination base station. Thus, even a base station having a second received electric field strength smaller than the first received electric field strength is included in the handover target base station, so that it is a base station that is moving away from the moving PHS user. However, if the corrected second received electric field strength is high, it is selected as the handover destination base station. Even if correction is performed by subtracting the correction value from the received electric field strength, if the received electric field strength is still high, there is a margin in the actual communication until the received electric field strength decreases by the amount of the subtracted correction value. Communication time can be ensured, and reception field strength fluctuations and noise due to fading are less likely to occur, so communication with higher call quality immediately after handover can be performed than a base station that is approaching but has low reception field strength. it can. In addition, the received electric field strength of the signal transmitted from the communicating base station is Predetermined Standard value Without exceeding the value obtained by adding a predetermined value to the reference value without measuring the received field strength of signals transmitted from the remaining base stations excluding the communicating base station among the plurality of base stations. The reception electric field strength measurement unit performs measurement of the reception electric field strength of the signal transmitted from the communicating base station, and the reception electric field strength of the signal transmitted from the communicating base station exceeds a predetermined reference value. When it is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether or not base station measurement is prohibited, and if base station measurement is prohibited, a base station in communication among a plurality of base stations is determined. Measurement of the received electric field strength of the signal transmitted from the communicating base station is performed by the received electric field strength measuring means without measuring the received electric field strength of the signal transmitted from the remaining base station. If not prohibited, the signal transmitted from multiple base stations The measurement of the signal field strength to perform the reception field strength measuring unit, is stored in the store means the reception field strength of the signal transmitted from each base station, Fixed time Since the base station measurement prohibition state is set, the reception field strength measurement unit measures the reception field strength of the signal transmitted from the communicating base station. Even if the reception level currently being communicated exceeds a predetermined reference value and there is no need to perform handover, the base station is measured at an excessive frequency and consumes extra power to talk time. It can be made not to affect.
[0013]
Further, the present invention provides a wireless terminal device that performs communication with a plurality of base stations provided at different fixed positions,
Received field strength measuring means for measuring received field strength of signals transmitted from a plurality of base stations;
Means for comparing the measured received field strength with a predetermined reference value and a value obtained by adding a predetermined value to the reference value;
A signal transmitted from each base station when the received electric field strength of the signal transmitted from the communicating base station is less than a value obtained by adding a predetermined value to the reference value in response to the output of the comparison means Is stored as the first received electric field strength, and when the received electric field strength of the signal transmitted from the communicating base station is equal to or lower than the reference value, the received electric field strength of the signal transmitted from each base station is Means for storing as a second received electric field strength, and subtracting the first received electric field strength from the second received electric field strength for each base station to obtain a received electric field strength difference;
Adding the obtained received electric field strength difference to the second received electric field strength to obtain a third received electric field strength;
Means for selecting a base station having the maximum received electric field strength from the determined third received electric field strengths;
The received electric field strength of the signal transmitted from the communicating base station is Predetermined Standard value Without exceeding the value obtained by adding a predetermined value to the reference value without measuring the received field strength of signals transmitted from the remaining base stations excluding the communicating base station among the plurality of base stations. The reception electric field strength measurement unit performs measurement of the reception electric field strength of the signal transmitted from the communicating base station, and the reception electric field strength of the signal transmitted from the communicating base station exceeds a predetermined reference value. When it is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether or not base station measurement is prohibited, and if base station measurement is prohibited, a base station in communication among a plurality of base stations is determined. Measurement of the received electric field strength of the signal transmitted from the communicating base station is performed by the received electric field strength measuring means without measuring the received electric field strength of the signal transmitted from the remaining base station. If not prohibited, the signal transmitted from multiple base stations The measurement of the signal field strength to perform the reception field strength measuring unit, is stored in the store means the reception field strength of the signal transmitted from each base station, Fixed time After the base station measurement prohibition state is set, the reception field strength measurement unit measures the reception field strength of the signal transmitted from the communicating base station. A wireless terminal device.
[0014]
According to the present invention, the first received electric field strength is compared with the second received electric field strength, the received electric field strength difference between the second received electric field strength and the first received electric field strength is obtained, and the obtained received electric field strength difference is calculated. A handover destination base station is selected from the third received electric field strengths by adding the second received electric field strength to the third received electric field strength. Since there is a time lag between selecting a handover destination base station and actually starting communication, if a base station that is approaching by a PHS user is selected as a handover destination, communication is performed from determination of the base station. When the base station that the PHS user is moving away from is selected as the handover destination, the reception field strength decreases from the base station determination to the start of communication. become. In addition, the received electric field strength of the signal transmitted from the communicating base station is Predetermined Standard value Without exceeding the value obtained by adding a predetermined value to the reference value without measuring the received field strength of signals transmitted from the remaining base stations excluding the communicating base station among the plurality of base stations. The reception electric field strength measurement unit performs measurement of the reception electric field strength of the signal transmitted from the communicating base station, and the reception electric field strength of the signal transmitted from the communicating base station exceeds a predetermined reference value. When it is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether or not base station measurement is prohibited, and if base station measurement is prohibited, a base station in communication among a plurality of base stations is determined. Measurement of the received electric field strength of the signal transmitted from the communicating base station is performed by the received electric field strength measuring means without measuring the received electric field strength of the signal transmitted from the remaining base station. If not prohibited, the signal transmitted from multiple base stations The measurement of the signal field strength to perform the reception field strength measuring unit, is stored in the store means the reception field strength of the signal transmitted from each base station, Fixed time Since the base station measurement prohibition state is set, the reception field strength measurement unit measures the reception field strength of the signal transmitted from the communicating base station. Even if the reception level currently being communicated exceeds a predetermined reference value and there is no need to perform handover, the base station is measured at an excessive frequency and consumes extra power to talk time. It can be made not to affect.
[0015]
By selecting a handover destination base station from the value obtained by adding the difference between the received field strength between the second received field strength and the first received field strength to the second received field strength as the third received field strength, It is possible to select a base station that assumes an increase / decrease in received electric field strength from when a station is selected until when communication is actually started. Therefore, since the optimum handover destination base station having a high received electric field strength can be selected at the start of communication, the number of handovers during a call can be suppressed, the influence on the call time can be minimized, and the call quality can be reduced. High communication can be performed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing a schematic configuration of a PHS 1 which is an embodiment of the present invention. The PHS 1 demodulates and modulates a signal transmitted / received by being connected to the antenna unit 3 and the antenna unit 3 that extends outward from the housing 2 to transmit / receive electromagnetic waves and is connected to the antenna unit 3. A wireless unit 4; an analog / digital converter 5 that mutually converts an analog signal and a digital signal; an audio processing unit 6 that controls sound related to band limitation; a microphone 7 and a speaker 8 that perform audio input and output; For example, a control unit 9 that is realized by a central processing unit, performs operation control of the wireless unit 4, analog / digital converter 5, audio processing unit 6, microphone 7, speaker 8, and input information; A first memory (hereinafter referred to as a ROM) 10 for storing the operation program and a second memory (hereinafter referred to as a RAM) 11 for storing received information on each base station. Including the.
[0017]
The control unit 9 operates according to the program read from the ROM 10 and measures the electric field strength of signals transmitted from a plurality of peripheral base stations. The signal from the control unit 9 is converted into an analog signal by the analog / digital converter 5, modulated by the radio unit 4, and then frequency-converted and transmitted from the antenna unit 3.
[0018]
The base station identifier (hereinafter referred to as CSID), the received field strength and the slot information, which are base station information obtained as a result of measuring the received field strength from the neighboring base stations, are received by the antenna unit 3, and the received signal is transmitted by the radio unit. After being frequency-converted by 4, the signal is demodulated, converted to a digital signal so as to be processed by the controller 9 by the analog / digital converter 5, and sent to the controller 9. The base station information is arithmetically processed as data in the control unit 9 or stored in the RAM 11. The base station information stored in the RAM 11 is read out as necessary, and is calculated by the control unit 9. In response to the calculation result, the control unit 9 selects the handover destination base station and executes the handover.
[0019]
A method for selecting a handover destination base station according to an embodiment of the present invention will be described. In one embodiment of the present invention, a base station whose reception level is reduced in time series is excluded from selection, and a base station having a maximum reception level is selected from base stations whose reception level is increased in time series. Choose.
FIG. 2 is a diagram illustrating a concept of handover accompanying movement of PHS. The circles in FIG. 2 represent cells that are ranges in which the base stations 1 to 5 can perform good communication with the mobile station PHS, and the base station exists at the center of the circle. Therefore, the position on the circumference represents a point where the handover needs to be performed. The arrow 12 in FIG. 2 indicates the direction in which the PHS moves, and the symbols a, b, c, and d indicate the positions at which the base station information is measured and the measurement results are received while the PHS is moving. To express.
[0020]
Table 1 shows the received electric field strengths obtained as a result of the base station information measurement of the base stations 1 to 5 at the positions a, b, c, and d in FIG. The unit of the numerical value indicating the received electric field strength in Table 1 is [dBμV]. In the following description and each flowchart described later, the received electric field strength is referred to as a reception level.
[0021]
It is assumed that the PHS that is communicating with the base station 5 has moved in the direction indicated by the arrow 12. In the movement to the point a, the reception level 40 from the base station 5 at the point a is 40 or more obtained by adding the predetermined value 10 to the handover holding level 30 that is the reference value. Therefore, communication with the base station 5 can be continued. Therefore, while the PHS 1 moves to the point a, it is possible to secure a sufficient call time without consuming extra power. In this case, in the prior art, handover is performed to the base station 4 having the highest reception level, and power for handover is unnecessarily consumed when there is no need for handover.
[0022]
If the PHS moves further and reaches between a and b, the reception level is equal to or higher than the reference value, but is less than 40, which is a predetermined value added, so that there is a possibility that handover is likely to be affected by fading and the like. Get higher. Therefore, the neighboring base station information is measured, and the CSID and the first reception level for each base station, which are the received base station information, are stored in the RAM 11 as the last received base station information.
[0023]
When the PHS further moves to reach the point b, the point b is located on the circumference of a circle representing the cell of the base station 5, so that it is difficult to perform good communication with the base station 5, and the handover target base Station information measurement is started. As a result of the base station information measurement at the point b, the CSID and the second reception level are obtained for each base station as the currently received base station information. In the base station information received this time, the second reception level of the base station 4 is 55, which is the highest, but it is lower than the first reception level of 60. Removed from the station. Note that the base station 5 that is currently communicating is also excluded from the handover target base station because the second reception level is reduced to 30 compared to 40, which is the first reception level. This process selects a base station that needs to be handed over again, even if the reception level immediately after handover is high, such as a base station that is moving away from a moving PHS user. There is no longer to do.
[0024]
The remaining base stations 1 to 3 are all set as handover target base stations because the second reception level is higher than the first reception level. Among the base stations 1 to 3, since the second reception level of the base station 3 is the highest, 40, the base station 3 is selected as the handover destination base station at the point b.
[0025]
At this time, the second reception level 40 of the base station 3 is equal to or greater than the value 40 obtained by adding a predetermined value to the reference value, and the reception level is sufficiently high, so there is no need to measure the neighboring base station information. Therefore, as long as the reception level does not decrease, as described above, measurement of neighboring base station information is not performed and no extra power is required, so that the call can be continued and sufficient call time can be secured. it can. After the base station 3 is selected as the handover destination base station, the currently received base station information is stored in the RAM 11 as the previously received base station information to prepare for the next handover target base station information accompanying the movement of the PHS. When the PHS further moves from b to c and d, the same processing as described above is performed to select a handover destination base station.
[0026]
With the above processing, it is possible to minimize the influence on the call time, reduce the number of handovers during a call, and realize a call with high call quality.
[0027]
[Table 1]

[0028]
FIG. 3 is a flowchart for explaining the handover processing operation of the control unit 9 of the PHS 1 according to the embodiment of the present invention. In the flowchart, the terms “measurement” and “measurement search” are both used, but both terms are used in the same meaning, and in the following description, they are unified in the measurement.
[0029]
In step a1, when the communication is started, various initializations such as the base station information received at the previous communication are performed to set the communication state. In step a2, reception level measurement of the currently communicating base station is started by reception level measurement means for measuring the reception level. In step a3, the reception level is repeatedly measured for the reception signal currently being communicated. In step a4, it is determined whether or not the reception level has been measured a predetermined number of times. If the reception level cannot be measured a predetermined number of times, the process returns to the measurement of the reception level in step a3. If the reception level can be measured a predetermined number of times, the process proceeds to step a5, and the average value of the reception levels is calculated. In step a6, it is determined whether or not the handover activation condition is satisfied by means for comparing the measured reception level with a predetermined reference value. That is, it is determined whether or not the average value of the reception levels calculated in step a5 is equal to or less than a predetermined reference value for a certain time. Here, the predetermined reference value is a critical reception level that requires a handover called a handover holding level.
[0030]
If it is determined in step a6 that the average value of the reception level currently being communicated exceeds a predetermined reference value for a certain period of time, the process proceeds to step a7 without activating the handover. In step a7, it is determined whether or not a base station measurement activation condition is satisfied. That is, it is determined whether the reception level currently being communicated is less than a value obtained by adding a predetermined value to the reference value. Here, the predetermined value is a value determined based on the operation. When the reception level currently being communicated is less than a value obtained by adding a predetermined value to the reference value, it is determined in step a8 whether or not the base station measurement prohibition timer is operating, and the base station measurement prohibition timer When it is operating, the measurement of the neighboring base station information is not performed, and the process returns to step a3. If the base station measurement prohibition timer is not in operation, in step a9, the CSID and the reception level that are base station information transmitted by each base station are measured for a plurality of neighboring base stations. During measurement of neighboring base station information, the received base station information is stored in the RAM 11.
[0031]
In step a7, when the reception level currently being communicated is equal to or higher than a value obtained by adding a predetermined value to the reference value, the process returns to step a3. That is, when the reception level during communication is high and the call quality is good, the measurement of neighboring base station information is not performed. Therefore, no extra power is consumed. In step a9, after the measurement for each base station is completed, if the same base station information is received a plurality of times during the measurement, an average value is obtained as the reception level. In step a10, the average value of the CSID and the reception level for each base station, which is the received base station information, is set as the first reception level, and stored as the previous reception base station information in the RAM 11, which is a storing means.
[0032]
In step a11, a base station measurement prohibition state is set for a predetermined time (T seconds). T seconds is a value determined based on the operation. The purpose of setting the base station measurement prohibition state for a certain period of time is that the reception level currently being communicated exceeds the predetermined reference value and there is no need to perform handover, but the base station is not frequently used. The station measurement is performed so that extra power is consumed so as not to affect the talk time. In step a11, after setting the base station measurement prohibition time for T seconds, the process returns to the reception level measurement of the communicating base station in step a3.
[0033]
If it is determined in step a6 that the average value of the reception level currently being communicated is equal to or less than the reference value for a certain time, the handover activation condition is established, and the process proceeds to step a12. In step a12, the handover target base station is measured under the same conditions as in the previous step a9 where the neighboring base stations were measured. During the measurement, the CSID and the reception level, which are information of the handover target base station, are set as the second reception level, and the current reception base station information is stored in the RAM 11 as the storing means.
[0034]
When the measurement of the handover target base station is completed, the process proceeds to step a13. In step a13, the CSID and the second reception level for each base station stored in the RAM 11 as the reception base station information this time, and the CSID and the first reception level for each base station stored in the RAM 11 as the previous reception base station information in the step a10. The control unit 9 compares the reception level. As a result of the comparison, if there is base station information with the same CSID in the current reception base station information and the previous reception base station information, the reception level difference between the second reception level and the first reception level for each base station that matches. Is calculated. Further, as a result of comparison, if there is no base station information having the same CSID in the current reception base station information and the previous reception base station information, the current reception base station information is stored in the RAM 11 as the previous reception base station information.
[0035]
In step a14, the base station whose second reception level is lower than the first reception level, that is, whose second reception level is lower than the first reception level, is excluded from the handover target base station. In step a15, a base station having the maximum second reception level is selected as a handover destination base station from base stations having a second reception level higher than the first reception level.
[0036]
In step a16, after the handover destination base station is selected, the current reception base station information obtained as a result of the handover target base station measurement is stored in the RAM 11 as the previous reception base station information. In step a17, a handover process is performed on the handover destination base station selected in step a15. In step a18, it is determined whether or not the handover process is successful. When the communication is notified from the handover destination base station and the handover process is successful, the process proceeds to step a19 and the previous reception base station of the handover destination base station is obtained. Information is initialized, and a communication state is established with a new base station that has succeeded in handover. In step a19, when communication is established with a new base station, the process returns to step a3 for measuring the reception level of the currently communicating base station, and proceeds to the subsequent steps.
[0037]
If the handover process fails in step a18, the process proceeds to step a20, where a process of returning (switching back) to the base station with which communication was performed before the handover process was started is performed, and communication is restored in step a21. If the switch-back process is successful, communication with the base station with which communication was performed before the handover process is resumed, the process returns to step a3 for measuring the reception level of the currently communicating base station, and proceeds to the subsequent steps. . If the switch-back process fails, communication cannot be performed with either the handover destination base station or the base station with which communication was performed before the handover process was started, and the communication ends.
[0038]
As another embodiment of the present invention, even when the second reception level is smaller than the first reception level, the channel may be selected as a handover destination base station. A method for selecting a handover destination base station according to another embodiment of the present invention will be described.
[0039]
Until the PHS user moves and reaches the point b, measures the base station information at the point b, and obtains the CSID and the second reception level for each base station as the currently received base station information as a result of the measurement, Since it is the same as that of the said embodiment, description is abbreviate | omitted. Base stations 4 and 5 which are base stations having a second reception level lower than the first reception level are selected from the base station information received this time. The corrected second reception levels 45 and 20 are obtained by subtracting a predetermined correction value 10 from 55 and 30 which are the second reception levels of the base stations 4 and 5, respectively. In another embodiment, even if the base station has a second reception level lower than the first reception level, the corrected second reception level is obtained, and the corrected second reception level is used as a numerical value for determining the handover destination base station. And are included in the handover target base station. Among the second reception levels of the base stations 1 to 3 whose second reception level is higher than the first reception level and the corrected second reception levels of the base stations 4 and 5, the reception level is 45, which is the highest. The base station 4 is selected as a handover destination base station.
[0040]
As described above, in another embodiment of the present invention, the base station 4 is selected as the handover destination base station at the point b. Although the base station 4 has a second reception level smaller than the first reception level and is moving away from the moving PHS user at the point b, the corrected second reception level is still obtained even if the correction value is subtracted. Is as high as 45. Since the actual reception level of the base station 4 is 55, which is the second reception level, in actual communication, there is a margin until the reception level is reduced by the subtracted correction value. Time can be secured. Also, since the reception level is high, fading noise is less likely to occur, and communication with higher call quality immediately after handover can be performed than a base station that is approaching but has a low reception level.
[0041]
FIG. 4 is a flowchart for explaining the handover processing operation of the PHS control unit according to another embodiment of the present invention. The flowcharts of the other embodiments are similar to those of the embodiment, and are the same except that step b14 and step a14 are different, and thus the duplicated description is omitted.
[0042]
In step b14 of the present embodiment, in the base station information obtained as a result of measuring the handover destination base station information, the second reception level is compared with the first reception level for each base station, and the second reception level is the first A base station smaller than the reception level is not excluded from the handover target base station, but a value obtained by subtracting the correction value from the second reception level is included in the handover destination target base station as a corrected second reception level. As in the case of the embodiment, the handover destination base station is selected in step b15 by selecting a reception level from the second reception level of the base station that is higher than the first reception level and the obtained corrected second reception level. Select the largest base station.
[0043]
As yet another embodiment of the present invention, a configuration may be adopted in which increase / decrease in the reception level of the handover destination base station is predicted and selected. A method for selecting a handover destination base station in still another embodiment of the present invention will be described.
[0044]
Until the PHS user moves and reaches the point b, measures the base station information at the point b, and obtains the CSID and the second reception level for each base station as the currently received base station information as a result of the measurement, Since it is the same as that of the said embodiment, description is abbreviate | omitted.
[0045]
For each base station, a first reception level is subtracted from the second reception level to obtain a reception level difference, and then the obtained reception level difference is added to the second reception level to obtain a third reception level. For example, in the base station 2 whose second reception level is higher than the first reception level, the first reception level 20 is subtracted from the second reception level 35 to obtain the reception level difference 15, and then the second reception level 35 The third reception level 50 is obtained by adding the reception level difference 15 to. In the base station 5 whose second reception level is lower than the first reception level, the first reception level 40 is subtracted from the second reception level 30 to obtain a reception level difference of minus 10, and then the second reception level 30 is reached. The reception level difference minus 10 is added to obtain the third reception level 20. Similarly, the third reception level is obtained for other base stations, and the base station 3 having the highest reception level is selected as the handover destination base station from the obtained third reception levels.
[0046]
In the handover process, there is a time lag between the selection of the handover destination base station and the actual start of communication. Therefore, when the base station that the PHS user is approaching is determined as the handover destination, the reception level increases between the base station selection and the communication start. Conversely, if the PHS user selects a base station that is moving away as a handover destination, the reception level decreases between the base station selection and the start of communication.
[0047]
As in still another embodiment of the present invention, a value obtained by adding the reception level difference is set as the third reception level, and the handover destination base station is selected from the third reception levels, and then the base station is selected. It is possible to select a base station that assumes an increase or decrease in reception level until communication is actually started. Therefore, it is possible to select an optimal handover destination base station having a high reception level at the time of starting communication, so that the number of handovers during a call is suppressed, the influence on the call time is minimal, and the call quality is high. Communication can be performed.
[0048]
FIG. 5 is a flowchart for explaining the handover processing operation of the PHS control unit according to still another embodiment of the present invention. Further, the flowcharts of the other embodiments are similar to those of the embodiment, and are the same except that step c14 and step a14 are different, and thus the duplicated description is omitted.
[0049]
In step c14 of the present embodiment, in the base station information obtained as a result of measuring the handover target base station information, the second reception level is compared with the first reception level for each base station, and the first reception level is compared with the first reception level. A value obtained by adding the reception level difference obtained by subtracting the reception level to the second reception level is defined as a third reception level. As in the embodiment, the handover destination base station is selected in step c15 by selecting the base station with the maximum reception level from the third reception levels.
[0050]
As described above, in each embodiment of the present invention, PHS is used as a wireless terminal device. However, the present invention is not limited to this, and a mobile phone device (Personal Digital Cellular) having a larger cell than PHS is used. It may also be a device that performs wireless communication, such as a taxi wireless device.
[0051]
【The invention's effect】
As described above, according to the present invention, the received electric field strength of a signal transmitted from a communicating base station is compared with a predetermined reference value and a value obtained by adding a predetermined value to the reference value. Measure the received field strength transmitted from each base station when the received field strength of the signal transmitted from the communicating base station exceeds the reference value plus a predetermined value in response to the output of the comparison result. Without continuing to communicate with the communicating base station, the received electric field strength of the signal transmitted from the communicating base station exceeds the reference value and is equal to or less than the value obtained by adding a predetermined value to the reference value, and there is no need for handover. When the received field strength of the signal transmitted from each base station is the first received field strength and the received field strength of the signal transmitted from the communicating base station needs to be handed over at a reference value or less, The received field strength of the signal transmitted from the station is set as the second received field strength. The first received electric field strength is compared with the second received electric field strength, and the base station whose second received electric field strength is smaller than the first received electric field strength is excluded from the handover target base stations. As a result, the second received electric field strength of the base station left as a handover target is only larger than the first received electric field strength, and the base station having the maximum second received electric field strength is selected as the handover destination base station. Since the selection is made, the received electric field strength of the selected base station is at a sufficiently high level, and the received electric field strength is not required to measure the neighboring base stations. Therefore, as long as the received field strength does not decrease, there is no need to measure the received field strength of signals transmitted from neighboring base stations and perform handover, so the number of handovers during a call is suppressed and the impact on the talk time is minimized. In addition, communication with high call quality can be performed.
In addition, the received electric field strength of the signal transmitted from the communicating base station is Predetermined Standard value Without exceeding the value obtained by adding a predetermined value to the reference value without measuring the received field strength of signals transmitted from the remaining base stations excluding the communicating base station among the plurality of base stations. The reception electric field strength measurement unit performs measurement of the reception electric field strength of the signal transmitted from the communicating base station, and the reception electric field strength of the signal transmitted from the communicating base station exceeds a predetermined reference value. When it is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether or not base station measurement is prohibited, and if base station measurement is prohibited, a base station in communication among a plurality of base stations is determined. Measurement of the received electric field strength of the signal transmitted from the communicating base station is performed by the received electric field strength measuring means without measuring the received electric field strength of the signal transmitted from the remaining base station. If not prohibited, the signal transmitted from multiple base stations The measurement of the signal field strength to perform the reception field strength measuring unit, is stored in the store means the reception field strength of the signal transmitted from each base station, Fixed time Since the base station measurement prohibition state is set, the reception field strength measurement unit measures the reception field strength of the signal transmitted from the communicating base station. Even if the reception level currently being communicated exceeds a predetermined reference value and there is no need to perform handover, the base station is measured at an excessive frequency and consumes extra power to talk time. It can be made not to affect.
[0052]
According to the present invention, the first received electric field strength is compared with the second received electric field strength. If the second received electric field strength is smaller than the first received electric field strength, the correction value is calculated from the second received electric field strength. A subtracted value is obtained as a corrected second received electric field strength, and a base station showing the maximum received electric field strength is selected from the second received electric field strength of the selected base station and the corrected second received electric field strength. Select as a handover destination base station. As described above, even if the second received electric field strength is smaller than the first received electric field strength, the base station is included in the handover target base station, so that the base station moving away from the moving PHS user is used. Even if it is, if the corrected second received electric field strength is high, it is selected as the handover destination base station. Even if correction is performed by subtracting the correction value from the received electric field strength, if the received electric field strength is still high, in actual communication, there is a margin until the received electric field strength decreases by the predetermined subtracted value. Since communication time can be secured and noise due to fading is less likely to occur, communication with higher call quality immediately after handover can be performed than a base station that is approaching but has a low received electric field strength.
[0053]
According to the present invention, the first received electric field strength is compared with the second received electric field strength, and the received electric field strength difference obtained by subtracting the first received electric field strength from the second received electric field strength is obtained. A handover destination base station is selected from the third received electric field strengths by adding the received electric field strength difference to the second received electric field strength as the third received electric field strength. Since there is a time lag between selecting a handover destination base station and actually starting communication, when a base station that is approaching by a PHS user is selected as a handover destination, communication starts from the selection of the base station. When the base station that the PHS user is moving away from is selected as the handover destination, the reception field strength decreases from the base station selection to the start of communication. become.
[0054]
A handover destination base station is selected from among the received field strength differences obtained by subtracting the first received field strength from the second received field strength as the third received field strength. Accordingly, it is possible to select a base station that assumes an increase or decrease in received electric field strength from when the base station is selected until when communication is actually started. Therefore, since the optimum handover destination base station having a high received electric field strength can be selected at the start of communication, the number of handovers during a call can be suppressed, the influence on the call time can be minimized, and the call quality can be reduced. High communication can be performed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a PHS 1 according to an embodiment of the present invention.
FIG. 2 is a diagram showing a concept of handover associated with PHS movement.
FIG. 3 is a flowchart for explaining a handover processing operation of the control unit 9 of the PHS 1 according to the embodiment of the present invention.
FIG. 4 is a flowchart for explaining a handover processing operation of a PHS control unit according to another embodiment of the present invention;
FIG. 5 is a flowchart illustrating a handover processing operation of a PHS control unit according to still another embodiment of the present invention.
[Explanation of symbols]
1 PHS
2 Case
3 Antenna part
4 radio parts
5 Analog / digital converter
6 Voice processing part
7 Microphone
8 Speaker
9 Control unit
10 ROM
11 RAM

Claims

In a wireless terminal device that performs communication with each base station provided at a plurality of different fixed positions,
Received field strength measuring means for measuring received field strength of signals transmitted from a plurality of base stations;
Means for comparing the measured received field strength with a predetermined reference value and a value obtained by adding a predetermined value to the reference value;
A signal transmitted from each base station when the received electric field strength of the signal transmitted from the communicating base station is less than a value obtained by adding a predetermined value to the reference value in response to the output of the comparison means Is stored as the first received electric field strength, and when the received electric field strength of the signal transmitted from the communicating base station is equal to or lower than the reference value, the received electric field strength of the signal transmitted from each base station is Store means for storing as the second received electric field strength;
A base station having a second received electric field strength greater than the first received electric field strength is selected, and among the base stations having a second received electric field strength greater than the first received electric field strength, the base having the maximum second received electric field strength. Means for selecting a station;
When the received field strength of a signal transmitted from a base station in communication exceeds a predetermined reference value and exceeds a value obtained by adding a predetermined value to the reference value, a base station in communication is excluded from a plurality of base stations The reception field strength of the signal transmitted from the communicating base station is measured by the reception field strength measurement means without measuring the reception field strength of the signal transmitted from the remaining base station. When the received electric field strength of the signal transmitted from the base station exceeds a predetermined reference value and is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether the base station measurement is prohibited, If station measurement is prohibited, the signal is transmitted from the communicating base station without measuring the received field strength of signals transmitted from the remaining base stations other than the communicating base station among the plurality of base stations. Measurement of signal reception field strength is performed on the reception field strength measurement means. If the base station measurement is not prohibited, the reception field strength measurement unit measures the reception field strength of signals transmitted from a plurality of base stations, and the reception field strength of the signals transmitted from each base station is determined. Store means to store, after setting the status of the base station measurements prohibited for a predetermined time, and means for Ru was performed on the reception field strength measuring means measures the reception field strength of a signal transmitted from the base station in communication A wireless terminal device.

In a wireless terminal device that performs communication with each base station provided at a plurality of different fixed positions,
Received field strength measuring means for measuring received field strength of signals transmitted from a plurality of base stations;
Means for comparing the measured received field strength with a predetermined reference value and a value obtained by adding a predetermined value to the reference value;
A signal transmitted from each base station when the received electric field strength of the signal transmitted from the communicating base station is less than a value obtained by adding a predetermined value to the reference value in response to the output of the comparison means Is stored as the first received electric field strength, and when the received electric field strength of the signal transmitted from the communicating base station is equal to or lower than the reference value, the received electric field strength of the signal transmitted from each base station is Means for storing as a second received field strength;
Selecting a base station having a second received electric field strength smaller than the first received electric field strength, subtracting a predetermined correction value from the second received electric field strength of the selected base station to obtain a corrected second received electric field strength;
A base station having a second received field strength greater than the first received field strength is selected, and the received field strength is selected from the second received field strength of the selected base station and the calculated corrected second received field strength. Means to select the base station that is the largest,
When the received field strength of a signal transmitted from a base station in communication exceeds a predetermined reference value and exceeds a value obtained by adding a predetermined value to the reference value, a base station in communication is excluded from a plurality of base stations The reception field strength of the signal transmitted from the communicating base station is measured by the reception field strength measurement means without measuring the reception field strength of the signal transmitted from the remaining base station. When the received electric field strength of the signal transmitted from the base station exceeds a predetermined reference value and is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether the base station measurement is prohibited, If station measurement is prohibited, the signal is transmitted from the communicating base station without measuring the received field strength of signals transmitted from the remaining base stations other than the communicating base station among the plurality of base stations. rows measurement of the reception field strength of the signal to the reception field strength measuring means If the base station measurement is not prohibited, the reception field strength measurement unit measures the reception field strength of signals transmitted from a plurality of base stations, and the reception field strength of the signals transmitted from each base station is determined. Store means to store, after setting the status of the base station measurements prohibited for a predetermined time, and means for Ru was performed on the reception field strength measuring means measures the reception field strength of a signal transmitted from the base station in communication A wireless terminal device.

In a wireless terminal device that performs communication with each base station provided at a plurality of different fixed positions,
Received field strength measuring means for measuring received field strength of signals transmitted from a plurality of base stations;
Means for comparing the measured received field strength with a predetermined reference value and a value obtained by adding a predetermined value to the reference value;
A signal transmitted from each base station when the received electric field strength of the signal transmitted from the communicating base station is less than a value obtained by adding a predetermined value to the reference value in response to the output of the comparison means Is stored as the first received electric field strength, and when the received electric field strength of the signal transmitted from the communicating base station is equal to or lower than the reference value, the received electric field strength of the signal transmitted from each base station is Means for storing as a second received field strength;
For each base station, subtract the first received field strength from the second received field strength to obtain the received field strength difference,
Adding the obtained received electric field strength difference to the second received electric field strength to obtain a third received electric field strength;
Means for selecting a base station having the maximum received electric field strength from the determined third received electric field strengths;
When the received field strength of a signal transmitted from a base station in communication exceeds a predetermined reference value and exceeds a value obtained by adding a predetermined value to the reference value, a base station in communication is excluded from a plurality of base stations The reception field strength of the signal transmitted from the communicating base station is measured by the reception field strength measurement means without measuring the reception field strength of the signal transmitted from the remaining base station. When the received electric field strength of the signal transmitted from the base station exceeds a predetermined reference value and is equal to or less than a value obtained by adding a predetermined value to the reference value, it is determined whether the base station measurement is prohibited, If station measurement is prohibited, the signal is transmitted from the communicating base station without measuring the received field strength of signals transmitted from the remaining base stations other than the communicating base station among the plurality of base stations. Measurement of signal reception field strength is performed on the reception field strength measurement means. If the base station measurement is not prohibited, the reception field strength measurement unit measures the reception field strength of signals transmitted from a plurality of base stations, and the reception field strength of the signals transmitted from each base station is determined. Store means to store, after setting the status of the base station measurements prohibited for a predetermined time, and means for Ru was performed on the reception field strength measuring means measures the reception field strength of a signal transmitted from the base station in communication A wireless terminal device.