JP2010166517A - Radio base station and radio terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a radio base station capable of avoiding delay caused by retransmission or waste of radio resources. <P>SOLUTION: A radio base station is a radio base station 2 for performing radio communications with radio terminals 3, 4, 5 accommodated within its own cell 1 and includes a transmission section for transmitting a downlink signal after appropriately changing the length of a synchronizing signal on the basis of states of communications with the radio terminals 3, 4, 5 so as to extend the length of the synchronizing signal for facilitating establishment of synchronism with a signal received at a radio terminal in the case where the state of a communication with the radio terminal is adverse. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radio base station in a cellular radio system.

  Conventionally, when a wireless terminal receives a control channel from a wireless base station intermittently in a standby state, the wireless terminal determines a reception state based on determination information such as electric field strength and presence / absence of errors in received data. The wireless terminal receives the control channel in a long cycle when the reception state is good, and switches to receive the control channel in a short cycle when the reception state becomes bad. As described above, Japanese Patent Application Laid-Open Publication No. 2004-151867 discloses a technique that enables reception of a control channel even when the reception state deteriorates.

JP-A-9-261153

  However, according to the above-described conventional technique, when the wireless terminal intermittently receives the control channel in the standby state, the wireless terminal changes the control channel reception cycle in accordance with the reception state, and thus synchronization may be lost. . For this reason, if the synchronization shift cannot be improved, there is a problem that the wireless link between the wireless terminal and the wireless base station is broken and the re-establishment process must be performed.

  The present invention has been made in view of the above, and obtains a radio base station capable of avoiding delay due to retransmission and waste of radio resources accompanying re-establishment processing of a radio link between the radio terminal and the radio base station. With the goal.

  In order to solve the above-described problems and achieve the object, the present invention provides a radio base station that performs radio communication with a radio terminal accommodated in its own cell, and performs synchronization based on a communication state with the radio terminal. Transmission means for transmitting a downlink signal by appropriately changing the length of the signal.

  According to the present invention, there is an effect that it is possible to avoid the delay due to retransmission and the waste of radio resources accompanying the re-establishment process of the radio link between the radio terminal and the radio base station.

  Embodiments of a radio base station according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a wireless system including a wireless base station according to the present invention. The radio base station 2 accommodates radio terminals 3, 4 and 5 in the cell 1. Here, communication in a TDMA / TDD (Time Division Multiple Access / Time Division Duplex) wireless system will be described as an example. For example, ARIB STD-T70 broadband mobile access system (HiSWANa).

  FIG. 2 is a diagram illustrating a configuration example of frames and signals in HiSWANa used in the present embodiment. The frame 10-2 includes a DL (Downlink) burst 20 and a UL (Uplink) burst 23.

  The DL (Downlink) burst 20 includes a broadcast channel (broadcast CH) 21 and a dedicated channel (dedicated CH) 22. A DL data unit 30 is obtained by encoding and modulating the DL burst 20. The DL data unit 30 time-multiplexes data 32-1 to 32-n for a plurality of wireless terminals. A DL (Downlink) signal 50 is obtained by adding a preamble 31 to the DL data unit 30. The preamble 31 stores a known symbol for synchronization.

  The UL burst 23 includes a dedicated channel (dedicated CH) 24 and a random access channel (RCH) 25. A UL data portion 40 is obtained by encoding and modulating the UL burst 23. The UL data unit 40 time-multiplexes preambles 41-1 to 41-m from a plurality of wireless terminals and data 42-1 to 42-m. The UL data unit 40 becomes a UL (Uplink) signal 51.

  Guard times 60, 61 and 62 are arranged before and after the DL signal 50 and the UL signal 51, respectively. The guard times 60, 61, and 62 absorb processing delays and avoid communication processing collisions in switching between downlink and uplink.

  FIG. 3 is a diagram illustrating a configuration example of the DL signal 50a including the preamble 31a longer than usual. The DL signal 50a has a constant number of data (the same length as the DL signal 50) so that the number of data stored in the DL data portion 30a is changed, and data 32-1 to 32-k (0 <k <n). And

  In the present embodiment, the radio base station 2 includes a transmission unit that can transmit a DL signal by changing the preamble length within a preset range. In addition, the wireless terminals 3, 4, and 5 include a receiving unit that can receive a DL signal whose preamble length is changed within a preset range.

  Next, a case where the radio base station 2 uses a preamble 31a longer than normal will be described. When a request for data transmission occurs when the wireless terminal 3 starts up or moves from another cell or when a wireless link between the wireless base station 2 and the wireless terminal 3 is not established, 2 and wireless link establishment processing. After establishing the wireless link, the wireless terminal 3 transmits a bandwidth allocation request to the wireless base station 2 through the random access channel 25. The radio base station 2 receives the band allocation request from the radio terminal 3 and notifies the radio terminal 3 of the band allocated in the broadcast channel 21 when the band can be allocated. The wireless terminal 3 recognizes that the band has been allocated and transmits data to the wireless base station 2.

  Here, when the wireless base station 2 does not receive the frame storing the bandwidth allocation request of the wireless terminal 3 due to some factors such as deterioration of the wireless environment or loss of synchronization, or when the wireless terminal 3 receives from the wireless base station 2 When the band allocation is not received, the radio terminal 3 retransmits the band allocation request to the radio base station 2. In this case, the radio base station 2 recognizes that the received band allocation request is a retransmission, gives a preamble 31a longer than normal in the next DL signal 50a, and allocates a band to the radio terminal 3 to the broadcast channel 21. Store and send.

  After detecting the DL signal 50a, the wireless terminal 3 performs frame synchronization and AFC (Automatic Frequency Control) using the preamble 31a as reception processing, and then performs decoding processing. In the wireless terminal 3, by using the preamble 31a which is longer than usual, the accuracy of carrier frequency deviation compensation is improved, and synchronization can be easily achieved. Further, the wireless terminal 3 is notified of the band allocation to the wireless terminal 3 through the broadcast channel 21, so that the transmission data is stored in the dedicated channel 24 as transmission processing, and after performing encoding and modulation processing, the wireless terminal 3 Transmit to base station 2.

  It is assumed that the radio terminal 3 is set in advance so that the preamble is variable and the length range value so that DL signals having different preamble lengths can be received. As a setting method, for example, initial data is set and read when the wireless terminal 3 is activated. As for the length of the preamble, two values, that is, a normal preamble and a preamble longer than normal may be used, or a minimum value and a maximum value may be set, and may be appropriately changed within the range.

  As described above, in the present embodiment, when the radio base station 2 does not receive a frame storing the bandwidth allocation request of the radio terminal 3, or when the radio terminal 3 allocates a bandwidth from the radio base station 2. If not received, the wireless terminal 3 retransmits the bandwidth allocation request to the wireless base station 2. In this case, the radio base station 2 recognizes that the received bandwidth allocation request is retransmission, and transmits the next DL signal 50a with the preamble 31a longer than usual added. Thereby, in the radio terminal 3 that has received the DL signal 50a to which the preamble 31a longer than usual is received, the accuracy of carrier frequency deviation compensation is improved by using the preamble 31a, and synchronization can be easily achieved. Therefore, it is possible to avoid delay due to repeated retransmissions and waste of radio resources due to re-establishment of the link between the radio terminal 3 and the radio base station 2.

Embodiment 2. FIG.
In the present embodiment, when the wireless terminals 3 to 5 are in a standby state and in an intermittent reception state, the wireless base station 2 gives a preamble 31a longer than usual when the wireless terminals 3 to 5 receive broadcast information. To do. A different part from Embodiment 1 is demonstrated.

  FIG. 4 is a diagram illustrating a frame transmitted by the radio base station and an intermittent reception cycle of the radio terminal. For example, the wireless terminal 3 is activated at the timing of the frames 70-2 and 70-q, and receives broadcast information.

  Next, a case where the radio base station 2 uses a preamble 31a longer than normal will be described. The radio terminals 3 to 5 accommodated in the cell 1 by the radio base station 2 receive broadcast information stored in the broadcast channel 21 from the radio base station 2 at the same intermittent reception period when transitioning to the intermittent reception state. The radio base station 2 uses the preamble 31a longer than usual only during the intermittent reception period in which the radio terminals 3 to 5 receive the broadcast information. For example, the wireless base station 2 holds the value of the intermittent reception cycle of the wireless terminals 3 to 5 in advance by setting the initial data at the time of activation. Generally, in the intermittent reception state, synchronization is likely to be out of sync as compared to the constant reception state. However, when the wireless base station 2 transmits a preamble 31a longer than usual, the wireless terminals 3 to 5 transmit the preamble 31a. Use makes it difficult to lose synchronization.

The radio base station 2 may determine the length of the preamble regardless of the length of the intermittent reception cycle of the radio terminals 3 to 5, or may change the length of the preamble according to the length of the intermittent reception cycle. FIG. 5 is a diagram illustrating the preamble length when the preamble length is changed according to the intermittent reception cycle. For example, in the range where the intermittent reception cycle t is “T ₀ <t ≦ T ₁ ”, the length of the preamble is set to “length # 1”. The information shown in FIG. 5 is assumed to be held in advance between the wireless base station 2 and the wireless terminals 3 to 5 before shifting to the intermittent reception state.

  As described above, in the present embodiment, the radio base station 2 adds the preamble 31a longer than normal to the DL signal 50a in the intermittent reception period of the radio terminals 3 to 5 and transmits it. As a result, the wireless terminals 3 to 5 that have received the DL signal 50a to which the preamble 31a longer than normal is received are unlikely to be out of synchronization by using the preamble 31a. It is possible to avoid waste of radio resources associated with the re-establishment process of the link between the radio base stations 2.

  Since the present invention is a method for adaptively controlling the DL burst preamble, the present invention is not limited to the TDMA / TDD method illustrated in FIG. 1, and can also be applied to the TDMA / FDD method. Further, the description has been made on the assumption that a known symbol called a preamble is added to the head of the DL burst. However, in principle, the known symbol may be arranged anywhere in the DL burst, and the known symbol is included in the DL burst received by the wireless terminal. The present invention can be widely applied to a wireless transmission system to which is assigned.

Embodiment 3 FIG.
In the present embodiment, in the radio base station 2, AFC is performed using the preambles 41-1 to 41-m of the UL signal 51, and when the carrier frequency deviation is larger than the threshold, the next DL signal 50a is longer than usual. A preamble 31a is assigned. A different part from Embodiment 1 is demonstrated.

  When a request for data transmission is generated, the wireless terminal 3 transmits a bandwidth allocation request to the wireless base station 2 through the random access channel 25. The radio base station 2 performs frame synchronization using the preambles 41-1 to 41-m of the UL signal 51, performs AFC, and performs decoding processing. If the carrier frequency deviation is larger than the threshold value as a result of performing AFC, the radio base station 2 transmits the next DL signal 50a with the preamble 31a longer than normal added. The radio base station 2 presets a carrier frequency deviation threshold value used for determining whether or not to give a longer preamble 31a than usual. The setting method is, for example, set to initial data and read when the radio base station 2 is activated. When the wireless base station 2 recognizes that the communication state with the wireless terminal 3 is not good, the wireless base station 2 gives a preamble 31a longer than usual and transmits it, so that the wireless terminal 3 transmits the preamble 31a. Use makes it difficult to lose synchronization.

  The radio base station 2 may set only one threshold or may set a plurality of thresholds and change the length of the preamble according to the magnitude of the carrier frequency deviation. FIG. 6 is a diagram illustrating the length of the preamble when the length of the preamble is changed according to the magnitude of the carrier frequency deviation. A case where three threshold values are set and four preamble lengths are set is shown. For example, in the range where the frequency deviation r is “r <threshold 1”, the length of the preamble is “length # 1”.

  As described above, in the present embodiment, the wireless terminal 3 transmits a bandwidth allocation request to the wireless base station 2, and the wireless base station 2 receives the bandwidth allocation request and performs AFC, resulting in a carrier frequency deviation. If it is greater than the threshold value, the radio base station 2 transmits the next DL signal 50a with the preamble 31a longer than normal added. Thereby, in the wireless terminal 3 that has received the DL signal 50a to which the preamble 31a longer than normal is received, it is difficult to lose synchronization by using the preamble 31a. It is possible to avoid waste of radio resources associated with the re-establishment process between the two links.

  As described above, the radio base station according to the present invention is useful for a cellular radio system, and is particularly suitable for maintaining synchronization between a radio base station and a radio terminal.

It is a figure which shows the structural example of a radio | wireless system. It is a figure which shows the structural example of a flame | frame and a signal. It is a figure which shows the structural example of DL signal. It is a figure which shows the flame | frame which a wireless base station transmits, and the intermittent reception period of a wireless terminal. It is a figure which shows an intermittent reception period and the length of a preamble. It is a figure which shows the frequency deviation and the length of a preamble.

1 cell 2 radio base station 3, 4, 5 radio terminal 10-1, 10-2, 10-3 frame 20 DL burst 21 broadcast channel 22 dedicated channel 23 UL burst 24 dedicated channel 25 random access channel 30, 30a DL data part 31, 31a Preamble 32-1, ..., 32-k, ..., 32-n Data 40 UL data part 41-1, ..., 41-m Preamble 42-1, ..., 42-m Data 50, 50a DL signal 51 UL signal 60, 61, 62 Guard time 70-1, ..., 70-r Frame 80 Intermittent reception period

Claims (10)

A wireless base station that performs wireless communication with a wireless terminal accommodated in its own cell,
Based on the state of communication with the wireless terminal, transmission means for appropriately changing the length of the synchronization signal and transmitting a downlink signal,
A radio base station comprising: The transmitting means further includes
The length of a synchronization signal of a downlink signal to be transmitted next is changed to be longer than that during normal communication when a bandwidth allocation request retransmitted from a wireless terminal is received. Wireless base station. The transmitting means further includes
The radio base station according to claim 1 or 2, wherein when the downlink signal is transmitted while changing the length of the synchronization signal, the amount of user data is changed and transmitted. The transmission means includes
4. The transmission according to claim 3, wherein when the length of the synchronization signal is longer than that during normal communication, the amount of user data is reduced and the length of the downlink signal is the same as that during normal communication. Wireless base station. The transmitting means further includes
2. The downlink signal is transmitted by changing the length of the synchronization signal to be longer than that during normal communication in accordance with the intermittent reception cycle of the wireless terminal accommodated in the cell of the local station. The radio base station according to any one of -4. The transmission means includes
The radio base station according to claim 5, wherein a downlink signal is transmitted by appropriately changing the length of the synchronization signal based on the length of the intermittent reception cycle. The transmitting means further includes
When receiving an uplink signal from a wireless terminal, recognizing that the frequency is shifted by AFC, and when the carrier frequency deviation is equal to or larger than a set threshold, the length of the synchronization signal is made longer than that during normal communication. The radio base station according to any one of claims 1 to 6, wherein the radio base station transmits a downlink signal after changing. The transmission means includes
The radio base station according to claim 7, wherein a downlink signal is transmitted by appropriately changing the length of the synchronization signal based on the magnitude of the carrier frequency deviation. The transmission means includes
The radio base station according to claim 1, wherein the synchronization signal is ContinuousWave. A wireless terminal that performs wireless communication with the wireless base station according to claim 1,
Receiving means capable of receiving downlink signals to which synchronization signals having different lengths are attached;
A wireless terminal comprising:

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