Patent Application
20090197623
This application is based upon and claims the benefit of priority of the prior Japanese Patent Application 2008-024283, filed on Feb. 4, 2008, the entire contents of which are incorporated herein by reference.
The disclosures herein are directed to a base station and a known sequence transmitting method.
Wireless communications systems for transmitting different data in different time periods have been known.
One example of such is an OFDMA (Orthogonal Frequency Division Multiplex Access) wireless communications system which employs FFR (Fractional Frequency Reuse). For the communication, WiMAX technology may be used.
In WiMAX, control signals including a preamble are placed at the beginning of a wireless frame, and are transmitted from a base station with relatively high power so as to reach across the entire cell of the base station.
According to an example depicted in
In each of
With reference to
Within the DL sub-frame in
Similarly, in
Similarly, in
That is to say, according to the example of
In the example of the conventional technology depicted in
Then, based on the CINR value fed back from the mobile station, the base station determines to assign the mobile station to either the zone of RF=1 (i.e. T2 in
Note that
Patent Document 1: Japanese Laid-open Patent Application Publication No. H10-186944
Patent Document 2: Japanese Laid-open Patent Application Publication No. 2006-74325
However, during T2 and T3, a mobile station located within the cell of a given base station may experience different levels of interference caused by signals transmitted by neighboring base stations.
That is, during T2, neighboring base stations also transmit wireless signals in the same frequency band; during T3, however, the given base station and its neighboring base stations transmit wireless signals in different frequency bands, not sharing the same frequency band. Accordingly, the mobile station may be subject to stronger interference during T2, as compared to during T3.
In view of the above-mentioned problem, there is a need to provide a base station and a known sequence transmitting method that take into account transmission conditions of neighboring base stations.
According to an embodiment, a base station for transmitting data at the same frequency as that used by neighboring base stations during a first time period, and transmitting data at a different frequency from those used by the neighboring base stations during a second time period, includes a transmitting unit configured to transmit a first known sequence during the first time period and transmit a second known sequence during the second time period.
Additional objects and advantages of the embodiment will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The following embodiments relate to a base station for transmitting data at the same frequency as that used by neighboring base stations during a first time period, and transmitting data at a different frequency from those used by the neighboring base stations during a second time period, the base station including a transmitting unit configured to transmit a first known sequence during the first time period and transmit a second known sequence during the second time period.
Since the first known sequence is transmitted during the first time period and the second known sequence is transmitted during the second time period, a mobile station located within the cell of the base station is able to measure reception quality of the first known sequence to thereby measure the reception environment for the first time period as well as measure reception quality of the second known sequence to thereby measure the reception environment for the second time period. Thus, transmitting the first and second known sequences has great significance.
Based on the measured reception environments, the mobile station may determine whether it is more desirable to receive data in the first time period or in the second time period. As a matter of course, the measurement results may be sent (reported) to the base station, and the base station may determine to transmit data to the mobile station during the first time period or the second time period. At the time of reporting the measurement results, simply the measurement results as they stand may be transmitted to the base station. Alternatively, of the two time periods, a more desirable one for data transmission (the desirability is evaluated in terms of, for example, throughput and whether an applicable MCS or the like operates at high speeds) is selected based on the measurement results, and the selected time period may be reported as the measurement results.
Each of the first time period and the second time period may include multiple temporally-separated time periods.
The first known sequence is preferably transmitted in all or part of the frequency band used for data transmission during the first time period. Also, the second known sequence is preferably transmitted in all or part of the frequency band used for data transmission during the second time period. The frequency band used for transmitting the first known sequence may be wider than the frequency band used for transmitting the second known sequence.
The following explains a WiMAX wireless communications system employing FFR.
In each of
With reference to
After the UL sub-frame, a signal corresponding to the next frame is transmitted, and the signal may take the same format, i.e. T1, T2, T3-1, T3-2 and UL sub-frame. Thus, after the first frame, subsequent data may be sequentially transmitted using such a frame structure.
Within the DL sub-frame in
T1 and T2 are zones during which transmission at the same frequency used by neighboring base stations is allowed. T1 and T2 together may be referred to as a first time period during which transmission is made at the same frequency as that used by neighboring base stations. On the other hand, T3-1 and T3-2 are zones during which transmission at a different frequency from those used by neighboring base stations is allowed. T3-1 and T3-2 together may be referred to as a second time period during which transmission is made at a different frequency from those used by neighboring base stations. Note that, even if T1 and T2 are temporally separated from each other, these two together can be referred to as the first time period. Likewise, even if T3-1 and T3-2 are temporally separated from each other, these two together can be referred to as the second time period.
Similarly, within the DL sub-frame in
Similarly, within the DL sub-frame in
That is to say, according to the example of
As illustrated in
Multiple base stations may start T1 and T3-1 in sync with each other, and may end T2 and T3-2 out of synch with each other. By synchronizing the timings, it is-possible to avoid T2 of one base station from temporally overlapping T3-1 of another base station.
As illustrated in
As has been described above, the control signals (including a preamble) for RF=1 are (possibly) transmitted during Ti at the same frequencies as those used by neighboring base stations, as in the case of the data burst in T2. Accordingly, it can be said that the preamble in T1 and the data burst in T2 when RF=1 are transmitted under relatively similar transmission conditions. That is, in terms of making transmission in the same frequency band as that used by neighboring base stations, T1 and T2 have similar transmission conditions. In the same way, the control signals for RF=3 are transmitted during T3-1 under similar transmission conditions to that for those data burst during T3-2 when RF=3. That is, in terms of making transmissions at a different frequency band from that used by neighboring base stations, T3-1 and T3-2 have similar transmission conditions. Therefore, the reception quality (e.g. CINR and reception level) measured from the preamble included in the control signals for RF=1 is likely to be similar to the reception quality obtained for the data burst when RF=1. In the same way, the reception quality (e.g. CINR) measured from the preamble included in the control signals for RF=3 is likely to be similar to the reception quality obtained for the data burst when RF=3. The base station may receive as feedback the reception quality obtained by the mobile station. Based on the transmitted results (CINRs) of the reception quality measured from both preambles for RF=1 and RF=3, the base station (control unit) may determine to assign the mobile station to either the zone of RF=1 (i.e. T2 in
In addition, as illustrated in
Note that DL-MAP transmitted in T1 defines a transmission format of data to be transmitted in T2 and a transmission timing; and DL-MAP transmitted in T3-l defines a transmission format of data to be transmitted in T3-2 and a transmission timing.
Next are briefly described effects obtained by implementing the above mentioned structure in the first embodiment.
Assume that the difference in CINRs between RF=1 and RF=3 is −5 dB (see
Assume here that a mobile station is assigned to the zone of RF=3. The following describes how to determine an applicable MCS in this case.
As illustrated in
As described above with reference to
Now assume that a mobile station is assigned to the zone of RF=3 (i.e. T3-2) and ten slots in T3-2 are allocated to the mobile station for twenty successive frames.
Further assume that the CINR value changes continuously for the twenty frames, for example, 3 dB in the frame number 1, 5 dB in the frame number 2 and so on. The simulation conditions are that a ratio of RF=1 and RF=3 for transmitting ten slots is 1:1, and the number of transmitted symbols for 10 slots is 480 symbols, calculated from the following equation:
10 (slots)×24 (sub-channels)×2 (symbols)=480 (symbols).
In this case, according to the conventional technology described above with reference to
480 (symbols)×0.67˜320 (bits).
Based on this calculation, according to the conventional technology, the total amount of data transmission for the 20 frames is 20,000 bits, as seen from
On the other hand, consider the case where the correspondence between CINRs and MCSs depicted in
480 (symbols)×1.33˜640 (bits).
Based on this calculation, according to the present embodiment, the total amount of data transmission for 20 frames is 28,960 bits, as seen from
Throughput Improvement=(28960)/(20000)˜1.5 (times).
Thus, it can be understood that the present embodiment improves the throughput of data transmission.
Note that it is here assumed that MCSs are associated with CINRs in an optimal manner, and wireless link drops are not taken into account for the sake of simplification.
Consequently, according to the first embodiment, even if FFR is employed, it is possible to assign a mobile station to an optimal zone and determine an optimal MCS, whereby the throughput of data transmission is improved.
As has been described above, the first embodiment relates to a communication system employing FFR in which each base station performs data transmission in the full range of all available frequency band A during the zone of RF=1 (i.e. T1 and T2 in
As described below in a second embodiment, the control signals including a preamble for RF=1 and the control signals including a preamble for RF=3 may be placed together at the beginning of the downstream wireless frame. Also in this case, as in the first embodiment, the control signals including a preamble for RF=1 are transmitted in the full range of all available frequency band A as in the case of a corresponding data burst when RF=1. In addition, the control signals are transmitted with the same transmission power (or transmission power increased by the amount corresponding to a predetermined offset) as for the corresponding data burst when RF=1. In the same manner, the control signals including a preamble for RF=3 are transmitted in a different one-third (B, C or D) of the full range of all available frequency band A as in the case of a corresponding data burst when RF=3. In addition, the control signals are transmitted with the same transmission power (or transmission power increased by the amount corresponding to a predetermined offset) as for the corresponding data burst when RF=3.
Note that the data transmission when RF=1 and RF=3 may be performed with the same transmission power, or alternatively, the data transmission when RF=1 may be performed with less transmission power as compared to the data transmission when RF=3.
As described below in a fifth embodiment, within a single downstream wireless frame, the control signals including a preamble for RF=1 are transmitted during the zone of RF=1 and the control signals including a preamble for RF=3 are transmitted during the zone of RF=3. In this case, in order to increase the data burst regions, the transmission cycle of the control signals including these preambles may be varied in view of the fading environment and the like. Base stations may transmit the preambles for RF=1 and RF=3 at the same time. In this case, the remaining control signals may be transmitted in each frame. Furthermore, at least one of the two preambles (e.g. the preamble transmitted in T1) may be transmitted in each frame.
As described below in a sixth embodiment, the control signals including a preamble for RF=1 and the control signals including a preamble for RF=3 may be placed together at the beginning of a downstream wireless frame. In this case, in order to increase the data burst regions, the transmission cycle of the control signals including these preambles may be varied in view of the fading environment and the like. Some wireless frames may include a preamble for RF=1 but exclude a preamble for RF=3, and other wireless frames may include a preamble for RF=3 but exclude a preamble for RF=1. In such a case, the control signals for RF=1 and RF=3, except for the preambles, may be transmitted in each frame.
Further detailed description of embodiments are given below.
As described above, according to the first embodiment, the base station transmits a preamble for a cell center (i.e. RF=1) and a preamble for a cell edge (i.e. RF=3). On receiving these preambles, the mobile station measures a CINR from each preamble. The measurement results are sent back to the base station as feedback, and the base station assigns the mobile station to a transmission zone and determines an applicable MCS based on the measurement results of both CINRs for the cell center and cell edge.
As illustrated in
The base station 100 is a wireless base station used in an OFDMA wireless communications system employing FFR.
The base station 100 includes an antenna unit for transmitting and receiving wireless signals; a switch unit 1 for switching transmission and reception of signals; a wireless receiving unit 2 having a downconverter for amplifying a wireless signal and converting it into a baseband signal; a CP removing unit 3 for extracting and removing a CP from the baseband signal; an S/P converting unit 4 for converting a serial signal to a parallel signal in order to be subjected to an FFT process; an FFT process unit 5 for extracting data by subjecting an OFDMA signal to the FFT process; a P/S converting unit 6 for converting the output parallel signal into a serial signal; a pilot extracting unit 9 for extracting a pilot signal from the FFT-processed signal; a channel estimating unit 8 for estimating a propagation environment from the extracted pilot signal; a demodulating unit 7 for correcting and demodulating data using the propagation environment estimated by the channel estimating unit 8; and a decoding unit 10 for decoding the demodulated data.
The base station 100 further includes a MAC process unit 11 for converting the decoded data into MAC-PDU, MAC-SDU, IP packets and the like; an IP network interface unit 12 connected to an ASN-GW; a burst data creating unit 11a, included in the MAC process unit 11, for creating downstream and upstream burst mappings; an RF=l FCH DL/UL-MAP generating unit 13 for generating an FCH signal, a DL-MAP signal and an UL-MAP signal for RF=1; an RF=3 FCH DL/UL-MAP generating unit 22 for generating an FCH signal, a DL-MAP signal and an UL-MAP signal for RF=3; an encoding unit 14 for encoding signals sent from the burst data creating unit 11a, RF=1 FCH DL/UL-MAP generating unit 13 and RF=3 FCH DL/UL-MAP generating unit 22; an RF=1 pilot/preamble generating unit 15 for generating a downstream pilot signal and a downstream preamble signal for RF=1; and an RF=3 pilot/preamble generating unit 24 for generating a downstream pilot signal and a downstream preamble signal for RF=3.
The base station 100 further includes an RF=1 symbol mapper unit 16 for converting an encoded signal for RF=1 and a signal from the RF=1 pilot/preamble generating unit 15 into symbols using an applicable MCS and mapping the converted symbols; an RF=3 symbol mapper unit 23 for converting an encoded signal for RF=3 and a signal from the RF=3 pilot/preamble generating unit 24 into symbols using an applicable MCS and mapping the converted symbol; an S/P converting unit 17 for converting output signals obtained from the RF=1 and RF=3 symbol mapper units 16 and 23 from serial signals into parallel signals in order to be subjected to an IFFT process; an IFFT unit 18 for subjecting a signal to the IFFT process to convert it into an OFDMA signal; a P/S converting unit 19 for converting a parallel signal output from the IFFT unit 18 into a serial signal; a CP inserting unit 20 for inserting a CP; and a wireless transmitting unit 21 having an upconverter for converting a signal into a wireless signal and an amplifier.
The base station 100 is characterized by including the RF=3 FCH DL/UL-MAP generating unit 22, the RF=3 symbol mapper unit 23 and the RF=3 pilot/preamble generating unit 24, which generate control signals including a preamble, FCH, DL-MAP and UL-MAP for RF=3.
As illustrated in
The mobile station 200 includes an antenna unit for transmitting and receiving wireless signals; a switch unit 51 for switching transmission and reception of signals; a wireless receiving unit 52 having a downconverter for amplifying a wireless signal and converting it into a baseband signal; a CP removing unit 53 for extracting and removing a CP from the baseband signal; an S/P converting unit 54 for converting a serial signal to a parallel signal in order to be subjected to an FFT process; an FFT process unit 55 for extracting data by subjecting an OFDMA signal to the FFT process; a P/S converting unit 56 for converting the output parallel signal into a serial signal; a pilot extracting unit 59 for extracting a pilot signal from the FFT-processed signal; a channel estimating unit 58 for estimating a propagation environment from the extracted pilot signal; and a demodulating unit 57 for correcting and demodulating data using the propagation environment estimated by the channel estimating unit 58.
The mobile station 200 further includes a decoding unit 61 for decoding the demodulated data; an MAC process unit 63 for converting the decoded data into MAC-PDU, MAC-SDU, IP packets and the like; a frame synchronizing unit 60 for synchronizing a wireless frame based on a preamble signal; an RF=1 CINR measuring unit 62 for measuring a CINR using a preamble for RF=1 and data; an RF=3 CINR measuring unit 74 for measuring a CINR using a preamble for RF=3 and data; an upstream burst creating unit 63a, included in the MAC process unit 63, for mapping the measured CINR values in a specified upstream burst; an upper layer process unit 64 for performing a process related to an upper layer above the MAC process unit 63; and a human interface unit 65 that provides an interface for connecting signals from, for example, keybuttons, a microphone, or a speaker of the mobile station 200 to the upper layer process unit 64.
The mobile station 200 further includes an encoding unit 66 for encoding a signal from the upstream burst creating unit 63a; a pilot signal generating unit 67 for generating an upstream pilot signal; a symbol mapper unit 68 for converting a signal from the encoding unit 66 and a pilot signal from the pilot generating unit 67 into symbols; an S/P converting unit 69 for converting an output signal obtained from the symbol mapper unit 68 from a serial signal into a parallel signal in order to be subjected to an IFFT process; an IFFT unit 70 for subjecting a signal to the IFFT process to convert it into an OFDMA signal; a P/S converting unit 71 for converting a parallel signal output from the IFFT unit 70 into a serial signal; a CP inserting unit 72 for inserting a CP; and a wireless transmitting unit 73 having an upconverter for converting a signal into a wireless signal and an amplifier.
According to the first embodiment, as described above, in a downstream communication from the base station 100, the control signals including a preamble for RF=1 are placed in the zone of RF=1 (i.e. specifically, in T1 out of T1 and T2 of
The mobile station 200 is particularly characterized by including the RF=3 CINR measuring units 74 to obtain the CINR measurement result for RF=3; and the upstream burst creating unit 63a to feed back the RF=3 CINR measurement result together with the RF=1 CINR measurement result to the base station 100.
As illustrated in
Note that the preambles and MAP information transmitted in T1 and T3-1 are broadcast, which can thereby be received by multiple mobile stations located within the cell of the base station.
The base station 100 illustrated in
Next, after receiving at the wireless receiving unit 52 the wireless signal transmitted from the base station 100, the mobile station 200 removes the CP from the signal and converts the signal from a serial signal to a parallel signal. Then, the mobile station 200 performs the FFT process on the signal and divides it into signals of respective sub-carriers. Subsequently, both RF=1 preamble and RF=3 preamble are demodulated at the demodulating unit 57, and CINRs are measured from the preambles at the RF=1 and RF=3 CINR measuring units 62 and 74. The measured CINRs are sent to the upstream burst creating unit 63a, which maps the CINRs in upstream data. The CINRs included in the upstream data are then transmitted from the transmitting antenna of the mobile station 200 (Steps S3 and S4).
Next, the base station 100 receives the CINRs based on the preambles for RF=1 and RF=3 transmitted from the mobile station 200, and determines a zone for the mobile station 200 (i.e. either the zone of RF=1 or the zone of RF=3) and an applicable MCS (Steps S5 through S9).
One example of how the base station 100 assigns the mobile station to a zone is to use a threshold α. That is, if the CINR of the preamble for RF=1 is larger than the threshold α (Step S5: Yes), the base station 100 assigns the mobile station 200 to the zone of RF=1 (Step S6). If the CINR of the preamble for RF=1 is equal to or less than the threshold α (Step S5; No), the base station 100 assigns the mobile station to the zone of RF=3 (Step S8). Regarding how to determine an applicable MCS, one example is to use the correspondence between CINRs and MCSs (Steps S7 and S9) described above with reference to
Note that the operation of the base station 100 is implemented when the CPU of the DSP 100C (illustrated in
According to the first embodiment of the present disclosure, as described above with reference to
The second embodiment has the same structure and functions as those of the first embodiment above, and the following description focuses on a difference from the first embodiment.
According to the second embodiment, the preambles for RF=1 and RF=3 are placed together at the beginning of each wireless frame. Also in this case, as in the first embodiment, the control signals including the preamble for RF=1 are transmitted using the full range of all available frequency band A, as in the case of a corresponding data burst when RF=1. In addition, the control signals are transmitted with the same transmission power as for the corresponding data burst when RF=1. In the same manner, the control signals including the preamble for RF=3 are transmitted in a different one-third (B, C or D) of the full range of all available frequency band A, as in the case of a corresponding data burst when RF=3. In addition, the control signals are transmitted with the same transmission power as for the corresponding data burst when RF=3.
That is, as illustrated in each of
The third embodiment has the same structure and functions as those of the first embodiment above, and the following description focuses on a difference from the first embodiment.
According to the third embodiment, the preambles for RF=1 and RF=3 are placed at the beginning of the respective zones (i.e. in T1 out of T1 and T2 for RF=1; and in T3-1 out of T3-1 and T3-2 for RF=3). In order to increase the data burst regions (the zones for transmitting actual data), the preambles for RF=1 and RF=3 are transmitted by being included periodically, for example, in every other wireless frame, instead of in every wireless frame.
In this case also, as in the first embodiment, the control signals including the preamble for RF=1 are transmitted using the full range of all available frequency band A, as in the case of a corresponding data burst when RF=1. In addition, the control signals are transmitted with the same transmission power as for the corresponding data burst when RF=1. In the same manner, the control signals including a preamble for RF=3 are transmitted in a different one-third (B, C or D) of the full range of all available frequency band A, as in the case of a corresponding data burst when RF=3. In addition, the control signals are transmitted with the same transmission power as used for the corresponding data burst when RF=3.
That is, as illustrated in
In the case of the third embodiment, since the control signals including preambles for CINR measurements are included in every other wireless frame, a wireless frame not including the control signals is transmitted once every two wireless frames. For the wireless frame having no control signals, due to there being no need of the control signals, it is possible to provide larger data burst regions.
The fourth embodiment has the same structure and functions as those of the first embodiment above, and the following description focuses on a difference from the first embodiment.
According to the fourth embodiment, the preambles for RF=1 and RF=3 are placed together at the beginning of a wireless frame. In order to increase the data burst regions, the preambles for RF=1 and RF=3 are transmitted by being included periodically, for example, in every other wireless frame, instead of in every wireless frame.
In this case also, as in the first embodiment, the control signals including a preamble for RF=1 are transmitted using the full range of all available frequency band A, as in the case of a corresponding data burst when RF=1. In addition, the control signals are transmitted with the same transmission power as for the corresponding data burst when RF=1. In the same manner, the control signals including a preamble for RF=3 are transmitted in a different one-third (B, C or D) the full range of all available frequency band A, as in the case of a corresponding data burst when RF=3. In addition, the control signals are transmitted with the same transmission power as for the corresponding data burst when RF=3.
As illustrated in
In the case of the fourth embodiment as in the third embodiment, since the control signals including preambles for CINR measurements are included in every other wireless frame, a wireless frame not including the control signals is transmitted once every two wireless frames. For the wireless frame having no control signals, due to there being no need of the control signals, it is possible to provide larger data burst regions.
Next is described the fifth embodiment.
The fifth embodiment has the same structure and functions as those of the first embodiment above, and the following description focuses on a difference from the first embodiment.
According to the fifth embodiment, as in the third embodiment, the preambles for RF=1 and RF=3 are placed at the beginning of the respective zones. In order to increase the data burst regions, the transmission cycle of the control signals including these preambles may be varied in view of the fading environment and the like. In the case where the fading environment changes rapidly, the preambles for RF=1 and RF=3 are included in every wireless frame. On the other hand, the environment remains unchanged, the preambles for RF =1 and RF=3 are transmitted periodically, for example, once every ten wireless frames.
In order to evaluate the fading environment, for example, an average X of CINRs measured by the mobile station 200 and a standard deviation a can be used. If the quotient (σ/X) is large, the fading variation is considered fast, and thus the preambles for RF=1 and RF=3 may be included in every wireless frame. On the other hand, if the quotient (σ/X) is small, the fading variation is considered slow, and thus the preambles for RF=1 and RF=3 may be transmitted once every ten wireless frames.
Next is described the sixth embodiment.
The sixth embodiment has the same structure and functions as those of the first embodiment above, and the following description focuses on a difference from the first embodiment.
According to the sixth embodiment, as in the fourth embodiment, the preambles for RF=1 and RF=3 are placed together at the beginning of a wireless frame. In order to increase the data burst regions, the transmission cycle of the control signals including these preambles may be varied in view of the fading environment and the like. In the case where the fading environment changes rapidly, the preambles for RF=1 and RF=3 are included in every wireless frame. On the other hand, the environment remains unchanged, the preambles for RF=1 and RF=3 are transmitted periodically, for example, once every ten wireless frames.
In this case also, in order to evaluate the fading environment, for example, an average X of CINRs measured by the mobile station 200 and a standard deviation a can be used. If the quotient (σ/X) is large, the fading variation is considered fast, and thus the preambles for RF=1 and RF=3 may be included in every wireless frame. On the other hand, if the quotient (σ/x) is small, the fading variation is considered slow, and thus the preambles for RF=1 and RF=3 may be transmitted once every ten wireless frames.
All examples and conditional language used herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority or inferiority of the invention. Although the embodiment of the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-024283 | Feb 2008 | JP | national |
