JPH11341540A - Cdma antenna diversity system, base station device and cdma softer hand-off system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide excellent or more seamless softer hand-off between sectors or antenna diversity in the CDMA communication system. SOLUTION: This CDMA antenna diversity system is used for a CDMA cellular radio telephone system that treats portable telephone subscribers in a cell consisting of a base station and a portable telephone exchange center 26 connected between the base station and an existing public telephone line network 27. Two antennas in the cell receive a transmission signal from mobile bodies 51, 52, 53, 54 and either of the two reception signals received by the two antennas in the cell with better reception sensitivity is selected. The cell 60 is divided into plural sectors X, Y, Z, W and each sector is covered with at least three antennas 401, 411, 421.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to code division multiplexing (Co).
In particular, the present invention relates to an antenna diversity technique and a softer handoff technique for a CDMA communication system.

[0002]

2. Description of the Related Art At present, mobile phones have become popular, and the mobile phone system is based on frequency division multiplexing (Frequency Division Multi) using different frequencies (wireless channels) for each user.
ple Access (FDMA)) method and time division multiplexing (Time Divisio) in which the same frequency is shared by dividing time for each user.
n Multiple Access (TDMA)) or a combination thereof. Each mobile phone user divides "frequency" or "time" in a communication space to prevent overlapping interference with other users.

On the other hand, a code division multiplexing (CDMA) system using a spread spectrum communication system has been proposed as a basic technology of the next generation mobile telephone system. This CDM
The A system is basically a multiple access system using normal DS (direct spreading). The 9.6 kbps digitized voice code is encoded with various error correction codes, synchronization detection codes, and the like, QPSK modulated, and transmitted in a spread band.

In CDMA, since the same frequency can be used between adjacent cells (or sectors), signals can be simultaneously received and used from a plurality of base stations near a cell boundary. This function is called site diversity (macro diversity).

[0005] In order to realize the site diversity, FDMA or the like requires two sets of independent communication devices in a mobile body. However, in the CDMA system, radio waves are transmitted from a plurality of base stations at the same frequency, so that a mobile unit can receive two sets of signals simultaneously with only one receiver (however, two despreaders). Such a receiver is called "RAKE
Receiver ".

With the site diversity and the RAKE receiver, functions called soft handoff (between cells) and softer handoff (between sectors), which cannot be realized by a conventional mobile phone, can be realized at the same time. What is soft handoff?
This refers to a technology in which, when a base station is switched as the mobile unit moves, the switching is performed instantaneously so that the user does not know the switching (or communication is performed simultaneously with the new and old base stations at the time of switching). Soft handoff is not a very important technology if the only information transmitted is voice (voices require re-training with the codec, resulting in audio loss), but are indispensable for data communication using mobile phones Technology.

[0007] In land mobile communication such as a cellular phone as a mobile communication, a frequency band of about 800 MHz to 2 GHz is used. Since radio waves in these frequency bands reach an appropriate distance, and travel to some extent in the shadows of buildings, they are convenient for car phones and mobile phones, and are used in various countries. However, signals in the frequency band are well reflected by buildings and the like.

When a radio wave is reflected by a building, a plurality of radio wave paths from the transmitting side to the receiving side of the communication system are created. This is called multi-path. When multipath occurs, target radio waves arrive from multiple directions,
Since radio waves are waves having amplitude and phase, signals arriving from each direction cause interference with each other. In particular, the radio wave that has arrived at the receiver after being reflected by the building arrives later than the radio wave that has directly arrived, because of the detour.
In a typical city, the arrival time difference between a direct wave and a reflected wave is about several tens of microseconds, and when a wireless LAN or the like is assumed indoors, it is about several tens of nanoseconds.

Two signals having different phases arrive at the antenna of the receiver due to the time lag. Then, when the phases match well, the signals strengthen each other, but when the phases are reversed, they weaken each other. In addition, assuming mobile communication, the sender or the receiver moves, so that the degree of phase combination changes from moment to moment, resulting in a drastic change in the amplitude of the synthesized signal. This is a phenomenon called “fading”.

When fading occurs, data errors increase significantly in the digital communication system. In particular, when the intensity of the direct wave and that of the reflected wave do not change so much, a phenomenon called a floor effect in which an error remains even if the signal power on the transmission side is increased can be confirmed. A diversity scheme is used as an example of fading countermeasures in the spread spectrum communication scheme.

[0011] Diversity is a general term for a method of receiving the same signal under various different conditions on the receiving side and selecting a better signal. Generally, a widely used method is to install a plurality of receiving antennas at distant locations and select the one with the greater signal strength received by both antennas.
This is spatial diversity. The present invention relates to this spatial diversity.

There are other types of diversity, such as frequency diversity, time diversity, and polarization diversity.
In the diversity method, there are some divisions depending on how to switch the reception signals of a plurality of systems. As the simplest method, there is a switching diversity for simply switching to a better condition at the input terminal of the receiver. In switching diversity, since noise is generated when the receiving system is switched, switching diversity after detection in which switching is performed after demodulation of a signal, maximum ratio combining diversity in which a plurality of systems are added without switching and an appropriate amount is proposed.

The sector division of the CDMA system is different from the conventional sector division. That is, conventional TDMA or FD
In the MA scheme, adjacent sectors use different channels or different frequencies, whereas CDMA
In the sector division of the system, there is no difference in frequency between adjacent channels.

In consideration of these characteristics, it is necessary to adopt a design method different from the conventional one in order to execute the softer handoff between sectors. Alternatively, it is necessary to adopt a different design method for antenna diversity.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a CD
In MA communication systems (different from conventional TDMA or FDMA systems), to provide better or more seamless inter-sector softer handoff or antenna diversity.

[0016]

SUMMARY OF THE INVENTION A CDMA antenna diversity system according to the present invention comprises a base station located in a cell and a mobile telephone switching center connected between the base station and an existing public telephone network. Used in a CDMA cellular radiotelephone system that handles mobile phone subscribers in a cell, two antennas in a cell receive a transmission signal from a mobile, and two received signals received by the two antennas , The cell is divided into a plurality of sectors, each sector being covered by at least three antennas, and the cell being divided by at least two antennas. A feature is that a part of the coverage area overlaps.

[0017] With this configuration, even when the mobile unit is near the boundary between adjacent sectors, the base station is provided with an antenna that makes this part a coverage area. Signals can always be received at a good level. Therefore, seamless softer handoff can be realized.

A base station apparatus used in such a system includes a plurality of antennas for receiving a transmission signal from a mobile body in a cell, a plurality of demodulators for demodulating signals received by the plurality of antennas, respectively. A plurality of RAKE fingers and an antenna / RAK for assigning processing of signals from a plurality of antennas to the plurality of RAKE fingers
An E-selector, a despreading code generator that applies a despreading code to a plurality of RAKE fingers, and a symbol combiner that combines the outputs of the plurality of RAKE fingers.

In one embodiment of the present invention, the plurality of antennas are at least three antennas covering a cell, and a part of the coverage area of at least two antennas is arranged to overlap. In addition, it is possible to further include a main antenna selector for selecting, as a main antenna, an antenna in which a signal received from a mobile object indicates a maximum level. Also, it is preferable to assign a larger number of RAKE fingers to the antenna selected as the main antenna than other antennas.

[0020]

FIG. 1 shows a configuration of a CDMA antenna diversity system according to an embodiment of the present invention. FIG. 1 shows an example where mobiles 51-54 are in sector X in cell 60. The base station device 30 is connected to a normal telephone switching network PSTN 27 via a mobile switching center MSC26.

The fan shapes (A), (B), and
(C) shows the coverage areas of the antennas 401, 411, and 421, respectively. However, this antenna coverage area is for explanation, and is drawn with a different size in the radial direction. However, this size may be the same or a size having an opposite relationship. However, what is important in FIG. 1 is that the sectors surrounded by the dotted lines are shifted in the circumferential direction. FIG. 1 shows an example in which a cell is divided into four, but the number of divisions of a sector is not an essential requirement of the present invention.

In FIG. 1, antennas 401, 411,
The coverage area of 421 is shifted in the radial direction. The entire area of sector X is covered by antenna 411, but antenna 401 covers a partial area of sector X and a partial area of sector Z. The antenna 421 is
It covers a partial area of sector X and a partial area of sector Y. Therefore, a part of the sector X is covered by the antenna 401, and the remaining area is covered by the antenna 421. The signals received by the antennas 401, 411, 421 are provided to the base station device 30.

FIG. 1 shows only three antennas 401, 411, and 421 for sector X. However, antennas are installed in the other three sectors W, Y, and Z so that their coverage areas overlap. Is done. In the case of a directional antenna, the reception sensitivity is the best when the moving object is captured at the center of the coverage area of the antenna.

Here, consider the case where softer handoff between sectors is performed when antenna 421 is not installed. Like the mobile terminal 54, when the mobile terminal exists at the boundary of the coverage area of the antenna 411 covering the sector X and the antenna (not shown) covering the sector Y, that is, when the mobile terminal exists at the boundary between sectors, the source sector X and the destination sector In both Y, the reception level by the antenna is reduced by, for example, 3 dB.

According to this embodiment, the antenna 421 is installed as shown in FIG. 1 so as to cover the boundary between the sector X and the sector Y, so that a decrease in the reception level at the time of soft handover is prevented. And high quality communication can be maintained. Note that the antenna 401 is provided so as to cover the boundary between the sector X and the sector Z.

As described above, in the diversity antenna beam arranging method of the present invention, a diversity antenna with less interference is selected by shifting the diversity coverage. As a result, it is possible to reduce the influence of radio waves emitted from other than the target mobile terminal, that is, interference.

FIG. 2 shows the antennas 401 (A) and 411.
(B), moving bodies 51, 52, 5 in 421 (C)
3 shows the strength of the received signal from 54. The vertical axis direction in the figure represents the amplitude of the received signal. From FIG. 2, it can be seen that the received signal strength from the mobile unit 51 is the largest at the antenna 411 (B). Similarly, mobile unit 5
2 also has an antenna 411 (B)
, The received signal strength from the mobile unit 53 is the largest received signal strength at the antenna 401 (A), and the received signal strength from the mobile unit 54 is the received signal strength at the antenna 421 (C). Is largest.

Next, CDMA according to an embodiment of the present invention
The detailed configuration of the base station device 30 used in the diversity antenna system will be described with reference to FIG. In FIG. 3, demodulators 40, 41, and 42 are receivers of a direct spread (DS) signal having the same configuration. Therefore, the internal configuration of the demodulator 41 will be described.

In the demodulator 41, a radio signal from the moving body 51 is received by the antenna 411. This received signal is input to a band pass filter (BPF) 412. Bandpass filter (BPF) 412 allows only the desired bandwidth of the received signal to pass. This is to prevent interference from unnecessary frequency bands and does not contribute to essential operations. The output from the band pass filter 412 is amplified by a low noise amplifier (LNA) 416. The output of the low noise amplifier (LNA) 416 is combined with the signal of cos ωt by the mixer 413, and then supplied to the low-pass filter (LPF) 414. The signal output from the low-pass filter (LPF) 414 is
The signal is converted into a digital signal by an analog / digital converter (A / D) 415 and supplied to the despreader 20.

In such a configuration, the signal received by the demodulator 41 from the mobile unit 51 is x (t) = S (t) co
It can be expressed in the form of sωt. Here, S (t) is a primary modulation signal, and cosωt is a carrier (carrier). After receiving x (t), the antenna 411 passes the band-pass filter 412 to remove unnecessary bandwidth. The output from the bandpass filter 412 is combined with cosωt by the mixer 413. As a result, the output y (t) of the mixer 413 is represented by the following equation.

Y (t) = S (t) cosωt = S (t) cos ² ωt = S (t) (１ ／ + ／ cos2ωt)

This y (t) is a low-pass filter 414
Is input to Since cos2ωt is in the high frequency band, it is filtered out by the bandpass filter 402.
As a result, the output z (t) of the low-pass filter 414 becomes
1 / 2S (t). This 1 / 2S (t) can be considered the same as S (t) by properly amplifying. Therefore, the primary modulation signal S (t) generated in the moving body 51 is obtained. This analog signal z (t) is converted to an analog / digital converter (A / D) 41
At 5, the light signal is converted into an optical signal and supplied to the despreader 20.

Next, the configuration of the despreader 20 will be described. The digital signal to despreader 20 is given by antenna / RA
It is input to the KE selector 21. The antenna / RAKE selector 21 outputs the outputs of the demodulators 40, 41, 42 to n RAKE fingers 203, 213,. . , 2n3. RAKE fingers 203, 21
3,. . , 2n3 are combined by a symbol combiner 22. This symbol combiner 22 acts as a maximum combining ratio combiner.

Output signal z (t) = S from demodulator 41
(T) = I (t) · pn (t) is the RAKE finger 20
3,213,. . , 2n3 assigned RA
In the KE finger, P from the despreading code generator 23
It is combined with N (t). Here, I (t) is the moving object 5
1, pn (t) is the mobile station 5
1 is the PN sequence used for spreading. The output of the RAKE finger 203 is expressed by the following equation. w (t) = S (t) · PN (t) = I (t) · pn (t) · PN (t)

As the RAKE finger 203, ie, the signal PN (t) input to the despreader on the receiving side, the same time waveform as the PN sequence pn (t) used for spreading on the transmitting side is used. Here, PN (t) is RAKE
This is a PN sequence used for despreading by the finger 203. As the PN sequence, a rectangular wave having a value of ± 1 at random is used. Therefore, the square of this is
Always 1 That is, when pn (t) = PN (t), the following equation is obtained.

W (t) = I (t) · pn ² (t) = I (t) · 1 The output of the RAKE finger 203 is w (t) =
I (t). On the other hand, when pn (t) ≠ PN (t), the following equation is obtained. w (t) = I (t) · 0

Therefore, by assigning a different PN sequence to each mobile unit, a target signal, for example, transmission data from the mobile unit 51, can be converted from a signal overlapping in terms of frequency and time with a RAKE finger. 203 can be picked up. That is, the PN sequence used in modulating the transmission data is used as a kind of keyword for separation.

Next, the operation of the antenna / RAKE selector 21 will be described. The receiving intensity information of the adjacent sector is sent to the main antenna selector 24 from the mobile body (mobile phone). The main antenna selector 24 determines whether the RAKE finger 203 and the demodulator 4
0, 41, or 42 is connected. As for the moving body 51, as shown in FIG. 2, the antenna 411 (B)
Indicates the maximum reception level. Therefore, the antenna 411
(B) is selected as the main antenna.

In this embodiment, four RAKE fingers are assigned to the main antenna, and two RAKE fingers are assigned to the other antennas.
Allocate RAKE fingers. Therefore, for example, RAKE fingers 203 and 213 are assigned to a received signal from antenna 401 and antenna 411
RAKE fingers 223, 233, 243, 253 are assigned to the received signal from the (main antenna).

Next, the antennas 401 and 41 shown in FIG.
In an antenna arrangement such as 1,421, antenna 4
Consider the case where the reception intensities of the signals from the mobiles MS1 and MS2 at 01, 411 and 421 are as follows. Antenna 401: Received intensity from MS1 large, Received intensity from MS2 small Antenna 411: Received intensity from MS1 large, Received intensity from MS2 large Antenna 421: Received intensity from MS1 small, Received intensity from MS2 large

In this case, signals from the antenna 401 and the antenna 411 are given to a plurality of RAKE fingers assigned to the mobile unit MS1. On the other hand, signals from antennas 411 and 421 are given to a plurality of RAKE fingers assigned to mobile unit MS2.

In FIG. 3, the symbol and timing information from the symbol combiner 22 are provided to a deinterleave circuit 30. The deinterleave circuit 30 converts a signal whose code has been rearranged by the interleave circuit prior to transmission at the transmitting end into an original code,
Re-sort. The symbol and timing information from the deinterleave circuit 30 is provided to a Viterbi decoder 31.

The Viterbi decoder 31 performs Viterbi decoding. The output of the Viterbi decoder 31 is provided to an error correction circuit 32, where an error in the data is corrected. The output from the error correction circuit 32 is provided to the microprocessor 33 as received data. Microprocessor 33
Controls a microphone / speaker 34 via a vocoder (speech encoder / demultiplexer) 35 and a DA / AD converter 36, and controls a key pad display 37.

FIG. 4 shows an example in which a 3-finger RAKE receiver is used as a RAKE receiver. The primary modulation signal is
Weighted PN for each finger is input to three fingers 51, 52, 53 and is output from weighting coefficient controller 54 to each finger.
The series is multiplied. The resulting signal is combined in phase by combiner 55 and output.

[0045]

As described above, according to the present invention,
In CDMA communication systems, good or more seamless inter-sector softer handoff or antenna diversity can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the arrangement of a diversity antenna according to an embodiment of the present invention.

FIG. 2 shows antennas 401 (A) and 411 in FIG.
(B) and 424 (C) are moving bodies 51, 52, 53 and 54.
FIG. 3 is a diagram showing signal strengths received from a computer.

FIG. 3 is a block diagram showing a configuration of a base station device used in a CDMA diversity antenna system according to an embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a three-finger RAKE receiver used in an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 20 despreader 21 antenna / RAKE selector switch 22 symbol combiner 23 despreading code generator 24 main antenna selector 26 mobile switching center (MSC) 27 telephone switching network (PSTN) 30 base station apparatus 40, 41, 42 demodulator 51, 52, 53, 54 Moving object W, X, Y, Z sectors 203, 213,... 2n3 RAKE fingers 401, 411, 421 Antennas 412 Bandpass filters 413 Mixers 414 Lowpass filters 415 Analog / digital converters 416 Low noise amplifier

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI H04J 13/00 D (71) Applicant 596077259 600 Mountain Avenue, Murray Hill, New Jersey 07974-0636U. S. A.

Claims (10)

[Claims] 1. A base station (40, 4) arranged in a cell.
1, 42) and the base station and the existing public telephone network (2
7), which is used in a CDMA cellular radio telephone system for handling cell phone subscribers in a cell comprising a cell phone switching center (26) connected to a mobile unit (51, 5).
2, 53, 54) are received by two antennas in the cell, and C selects which one of the two received signals received by the two antennas has the better reception sensitivity.
In the DMA antenna diversity system, the cell (60) includes a plurality of sectors (X, Y, Z, W)
And each of the sectors has at least three antennas (401,
411, 421), wherein a part of the coverage area of at least two antennas overlaps. 2. A plurality of mobile telephone subscribers in a cell comprising a base station arranged in a cell and a mobile telephone switching center connected between the base station and an existing public telephone network are handled. Used in CDMA cellular radiotelephone systems,
In a CDMA antenna diversity system in which a plurality of antennas in a cell receive an outgoing signal from a mobile body and select a reception signal having the best reception sensitivity among the plurality of reception signals, the cell includes at least three cells. A CDMA antenna diversity system covered by an antenna, wherein a part of a coverage area of at least two antennas overlaps. 3. The system according to claim 1, wherein the antenna is a directional antenna. 4. The system according to claim 1, wherein at least one antenna covers an adjacent sector or an adjacent cell. 5. The system according to claim 1, wherein the first antenna covers substantially the entire sector, the second antenna covers a partial area of the sector, and the third antenna covers the remaining area. System. 6. A CDMA cellular system for handling mobile phone subscribers in a cell comprising a base station arranged in a cell and a mobile phone switching center connected between said base station and an existing public telephone network. Two antennas in a cell receive a transmission signal from a mobile body, and are used in a radio telephone system. A reception signal having a better reception sensitivity among the two reception signals received by the two antennas is transmitted. In a CDMA softer handoff system of choice, the cell is divided into a plurality of sectors, each sector being covered by at least three antennas, and at least a part of the coverage area of the two antennas being overlapped. Characterized CDMA softer handoff system. 7. A plurality of antennas (401, 411, 421) for receiving transmission signals from mobiles in a cell, and a plurality of demodulators (40, 41, 42) for demodulating signals received by the plurality of antennas, respectively. ) And a plurality of RAKE fingers (203, 213,..., 2)
n3), an antenna / RAKE selector (21) for assigning processing of signals from the plurality of antennas to the plurality of RAKE fingers, and a despreading code generator (23) for applying a despreading code to the plurality of RAKE fingers. A base station apparatus for a CDMA antenna diversity system, comprising: a combiner (22) for combining outputs of the plurality of RAKE fingers. 8. The base station according to claim 6, wherein the plurality of antennas are at least three antennas covering a cell, and a part of a coverage area of at least two antennas overlaps with each other. apparatus. 9. A main antenna selector (24) for selecting, as a main antenna, an antenna having a maximum level of a signal received from a mobile unit.
Or the base station apparatus according to 8. 10. The base station apparatus according to claim 9, wherein a larger number of RAKE fingers are assigned to the antenna selected as the main antenna than other antennas.