BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a conceptual diagram of a communication system to which the invention is applied, and is a figure showing a system in which terminals MS perform asynchronous communication.
FIG. 1B is a conceptual diagram of a communication system to which the invention is applied, and is a figure showing a system in which terminals MS, clock-synchronized with a GPS, communicate without mediation of base stations or similar.
FIG. 2 is a figure showing the common terminal configuration of terminals MS in a communication system in which the terminals MS shown in FIG. 1A communicate asynchronously.
FIG. 3 is the signal format used in the communication system of the terminal configuration of FIG. 2.
FIG. 4 is the operation flow corresponding to the aspect of FIG. 2 and FIG. 3.
FIG. 5 shows the common terminal configuration of terminals MS in a communication system in which terminals MS shown in FIG. 1B are synchronized with the clock of a GPS.
FIG. 6 is the signal format used in the communication system of the terminal configuration of FIG. 5.
FIG. 7 is the operation flow corresponding to the aspect of FIG. 5.
FIG. 8 is an example of a signal format in the third aspect of the invention.
FIG. 9 is a (first) operation flow corresponding to the aspect of FIG. 8.
FIG. 10 is a (second) operation flow corresponding to the aspect of FIG. 8.
FIG. 11 is a figure showing an example of a signal format of the fourth aspect, in which, compared with the second aspect, priority control is performed enabling transmission within time slots.
FIG. 12 is a time chart figure explaining transmission collision avoidance in the fourth aspect.
FIG. 13 is a figure showing operation flow based on transmission rights.
FIG. 14 is a figure showing an example of a signal format explaining the fifth aspect.
FIG. 15 is a figure showing an example of a signal format explaining the sixth aspect.
Explanation of Symbols
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Aspects of the invention are explained below, referring to the drawings. The aspects are provided to facilitate understanding of the invention, and the technical scope of the invention is not limited to these aspects.
FIG. 1A and FIG. 1B are conceptual diagrams of a communication system to which the invention is applied. In the system shown in FIG. 1A, asynchronous communication by each mobile terminal (hereafter simply called “terminal”) MS is shown. On the other hand, in the system shown in FIG. 1B, communication is shown by each terminal MS, clock-synchronized with a GPS (Global Positioning System), without mediation of a base station or relay station.
FIG. 2 shows the terminal configuration common to terminals MS in a communication system in which each terminal MS shown in FIG. 1A performs asynchronous communication. FIG. 3 shows the signal format used in the communication system with the terminal configuration of FIG. 2.
The signal format shown in FIG. 3 is the result of addition of a CSMA function to a WiMAX standard downlink circuit. A plurality of subchannels are provided in the frequency axis direction, and in the time axis direction a preamble signal a, broadcast signal b, and burst data c are provided. The burst data c is frequency-divided and allocated to a plurality of subchannels. The example of FIG. 3 is an example in which the two terminals #0 and #1 perform time-division communication; carrier sensing is performed to confirm there is no transmission from the other terminal before performing transmission.
Returning to FIG. 2, the terminal configuration comprises a network interface portion 1; media access control (MAC) processing portion 2, which performs encoding, error correction, transmission region specification, and other processing of transmission data; a physical layer (PHY) processing portion 3; a wireless frequency transmission/reception (RF) portion 4; and a GPS reception portion 5.
The network interface portion 1 of the terminal configuration has external interface functions and transmission/reception functions with the MAC processing portion 2. The MAC processing portion 2 has resource management and MAC layer functions in WiMAX systems.
The PHY processing portion 3, as the transmission function portion, comprises a preamble signal generation portion 30 which generates a preamble pattern; a broadcast signal generation portion 31; a burst data generation portion 32; a modulation processing portion 33; a multiplex processing portion (MUX) 34; and an inverse fast Fourier transform portion (IFFT) 35.
In the preamble signal generation portion 30, generation of the preamble symbols specified by the MAC processing portion 2 is performed. The broadcast signal generation portion 31 processes transmission data from the MAC processing portion 2 to perform generation and PHY layer processing of prescribed broadband data according to instructions from the MAC processing portion 2. The burst data generation portion 32 performs PHY layer processing of transmission data according to instructions from the MAC processing portion 2.
The modulation processing portion 33 performs QPSK, BPSK, multivalue modulation, and other modulation of signals from the different generation portions. The multiplexing processing portion 34 performs multiplexing of signals from the different generation portions, according to usage region (multiplexing format) instructions from the MAC processing portion 2.
The inverse fast Fourier transform portion (IFFT) 35 performs fast Fourier transform and other processing according to parameters specified by the MAC processing portion 2. The fast Fourier transform output is then frequency-converted at wireless frequencies by the RF portion 4, and is transmitted from the antenna ANT.
On the other hand, the PHY processing portion 3 comprises, as reception functions, a path detection portion 36, fast Fourier transform (FFT) portion 37, preamble signal reception processing portion 38, broadcast signal reception processing portion 39, and burst data reception processing portion 40.
The path detection portion 36 provides a portion of demodulation functions, and has functions for detecting reception paths exceeding a certain threshold and transmitting to the FFT portion 37, and a function for notifying the MAC processing portion 2 of the path detection result. When the path detection portion 36 detects a reception path which exceeds the threshold, the state is a state in which there is transmission from another terminal, and so the MAC processing portion 2 executes control such that no transmission from the terminal is performed.
The FFT portion 37 performs fast Fourier transform and other processing. The preamble signal reception processing portion 38 has functions for detection of preamble signals transmitted by a transmission terminal and for synchronization, and has a function for notifying the broadcast signal reception processing portion 39 and MAC processing portion 2 of the timing.
The broadcast signal reception processing portion 39 has functions for reception processing of internal information in WiMAX, and for notification of the MAC processing portion 2.
The burst data reception processing portion 40 receives notification, via the MAC processing portion 2, of the contents of broadcast signals, and performs WiMAX reception processing for the notified region.
The RF portion 4 has transmission/reception functions for RF modulation of baseband signals of the PHY processing portion 3, and for demodulation from RF to baseband.
FIG. 4 shows the operation flow corresponding to the aspect of FIG. 2 and FIG. 3.
This is an example of ad-hoc communication between two terminals MS #0 and #1. When there is data for transmission by both terminals MS #0 and #1, it is assumed that terminal MS #0 first performs data transmission.
Terminal MS #0 transmits the preamble signal (step S2-1), transmits a common connection ID (step S2-2), and then transmits burst data transmission data on a plurality of subchannels (step S2-3).
On the other hand, terminal MS #1 performs carrier detection (step S3-1), and when a carrier is detected, transmission is not performed from terminal MS #1. At this time, when the preamble signal is received from terminal MS #0, timing synchronization with terminal MS #0 is performed (step S3-2).
When synchronization is secured, the data subchannel storage region (subchannel) is identified based on the common connection ID (step S3-3). Then, burst data is received from the identified storage region (step S3-4).
When carrier detection (step S3-1) ceases, a preamble signal is similarly transmitted from terminal MS #1 (step S4-1), a common connection ID is transmitted (step S4-2), and then burst data is transmitted over a plurality of subchannels (step S4-3).
On the other hand, terminal MS #0 similarly performs carrier detection (step S5-1), and when a carrier is detected, no transmission is performed from terminal MS #0. At this time, the preamble signal is received from terminal MS #1, and timing synchronization with terminal MS #1 is performed (step S5-2).
When synchronization is secured, the data subchannel storage region is identified based on the common connection ID (step S5-3). Then, burst data is received (step S5-4).
By repeating the above processing, data communication can be performed asynchronously between the terminals MS #0 and #1.
In this first aspect, by basing communication on the OFDM modulation method, characteristics related to mobility can be improved.
FIG. 5 shows the common terminal configuration of each of the terminals MS in a communication system in which each of the terminals MS shown in FIG. 1B is synchronized with a GPS clock. FIG. 6 is a signal format applied to a communication system in which communication is performed between terminals conforming to the terminal configuration of FIG. 5. And, FIG. 7 shows the flow of operation corresponding to the aspect of FIG. 5.
The aspect of a terminal MS shown in FIG. 5 has further added a GPS reception portion 5, but otherwise is configured similarly to the configuration shown in FIG. 2. An internal clock is generated based on the GPS clock received by the GPS reception portion 5, and the MAC processing portion 2 and PHY processing portion 3 operate in synchronization with this internal clock.
FIG. 6 shows the signal format in the second aspect, with the WiMAX standard downlink circuit unmodified.
Whereas in the first aspect previously explained, path detection (carrier sensing) is performed constantly during reception, in this second aspect, path detection (carrier sensing) is performed only at the timing for reception of a preamble signal (steps S3-1, S6-1).
In other words, as shown in the operation flow of FIG. 7, the terminal MS is configured such that when there is transmission data, if the result of path detection (steps S4-1, 4-2) indicates that the time slot is unused, transmission is performed in the next time slot (step S6-1). In this way, there is no need for time slot synchronization, and so the internal clock is generated based on the received clock from the GPS.
Whereas if the time slot space is freely usable then preamble detection must always be performed, as shown in the operation flow of FIG. 4 (steps S3-1, 5-1, 7-1), in this second aspect, it is sufficient to perform path detection (carrier sensing) only with the timing for receiving the preamble signal.
In this second aspect, communication reliability in synchronous communication can be improved.
FIG. 8 is an example of the signal format of a third aspect of the invention. FIG. 9 and FIG. 10 show the (first and second) operation flow corresponding to the aspect of FIG. 8.
This third aspect adds priority control to the second aspect. In the signal format of FIG. 8, the WiMAX standard downlink circuit is unchanged. That is, following the preamble signal a, a broadcast signal b provides notification of the data storage region based on a common connection ID. Then, burst data c, multiplexed in subchannels, is transmitted.
As shown in FIG. 9 and FIG. 10, a characteristic of this third aspect is the assumption of communication by for example terminal MS #0 and terminal MS #1. When the priority order is made higher for terminal MS #0, the next time slot for which transmission rights are granted is provided to terminal MS #0, and transmission rights are provided two time slots later to terminal MS #1. As a result, collision does not occur. That is, the order of priority is assigned from terminals with a high degree of urgency, and transmission collisions are avoided.
In FIG. 9, when terminal MS #1 receives signals from terminal MS #0 in steps S3-1 to 3-4, terminal MS #1 can perform transmission two time slots later (steps S5-1 to 5-3). Similarly, transmission rights are again provided to terminal MS #1 in time slot #8.
On the other hand, when terminal MS #0 receives signals from terminal MS #1 in steps S6-1 to 6-4, terminal MS #0 can perform transmission in the next time slot (#5).
In the flow of FIG. 9 and FIG. 10 processing is not performed in time for the time slot immediately following reception of signals from the other terminal, and so the time slot immediately following is skipped, and “the next time slot” means the time slot after this. For the terminal MS #1 with lower order of priority, this similarly means two time slots later.
FIG. 11 shows an example of the signal format for a fourth aspect, in which, as opposed to the second aspect priority control is performed enabling transmission within time slots. FIG. 12 is a time chart used to explain transmission collision avoidance in the fourth aspect.
In FIG. 11, the format of control signals a (including preamble signals and broadcast signals) and, following these, allocation of a plurality of information data signals b to subchannels, conforms to the MiMAX standard, similarly to the previous aspect.
FIG. 12 explains collision avoidance in the fourth aspect. In FIG. 12, R indicates the wait time, PT is the preamble signal, and BR is the broadcast signal. Other than R, similarly to the previously described aspect, the WiMAX standard downlink circuit is unchanged.
That is, different unique wait times R are set for the respective terminals in order to provide transmission rights to one terminal MS in one time slot.
In the example of FIG. 12, the wait times R are set so as to become larger in the order of the terminals MS #2, MA #1, MS #0.
Hence as shown in FIG. 11, in time slot #0 terminal MS #2 has transmission rights, in time slot #1 terminal MS #1 has transmission rights, and in time slot #2 terminal MS #0 has transmission rights.
FIG. 13 shows the operation flow based on these transmission rights. The three terminals MS #0, #1, #2 all have transmission data (steps S1-1, S1-2, S1-3).
As explained in FIG. 12, the wait time for terminal MS #2 is set to R=0. A wait time of R=0 means that the wait time is zero, and so terminal MS #2 performs path detection (step S2-1), and because a path is not detected (step S2-2), immediately performs transmission (steps S5-1 to S5-3).
On the other hand, during this period the other terminals MS #1 and #0 are performing frame leading path detection operations (steps S3, S4).
Hence preamble signals transmitted from terminal MS #2 are received (steps S3, S4), and so these perform synchronization and receive signals from terminal MS #2 (steps S6-1 to S6-2, 7-1 to S7-2).
Hence by keeping the wait time R within the OFDM guard interval time GI, transmission rights allocation can be set for a plurality of terminals MS.
In this way, in the fourth aspect, transmission collision avoidance is improved, and by reviewing periods in which transmission is possible, the efficiency of frequency utilization is improved.
FIG. 14 shows an example of a signal format explained in a fifth aspect.
In this aspect, compared with the fourth aspect, a plurality of subchannels are grouped, and within these, processing similar to that of the fourth aspect is performed.
That is, in FIG. 14, as an embodiment, every ten subchannels #0-9, #10-19, . . . , are grouped as single groups.
Then, for each group, wait times R are made different and set individually for terminals MS belonging to the group, similarly to the fourth aspect.
Thus in the example of FIG. 14, for the three terminals MS #0 to #2 belonging to the group of subchannels #0 to #9, transmission rights are provided to terminal MS #0 in time slot #0, to terminal MS #1 in time slot #1, and to terminal MS #2 in time slot #2. For the three terminals MS #3 to #5 belonging to the group of subchannels #10 to #19, transmission rights are provided to terminal MS #4 in time slot #0, to terminal MS #5 in time slot #1, and to terminal MS #3 in time slot #2.
In this fifth aspect, the characteristics of the OFDMA method are exploited, and transmission regions are divided by subchannel, so that transmission collision avoidance is achieved and terminal transmission efficiency can be improved.
FIG. 15 shows an example of a signal format used in explaining a sixth aspect.
In this aspect, an approach is taken in which two subgroups are transmission regions. In FIG. 15, a terminal MS uses its own terminal number or similar to determine as its groups two adjacent groups.
In FIG. 15, in for example two groups, of subchannels #0 to #9 and subchannels #10 to #19, the usage region is changed at each time slot. In subchannels #0 to #9, transmission rights are set in every slot, that is, at #0 and #2 for terminals MS #0 and #2. Similarly in subchannels #10 to #19, transmission rights are set in slot #1 for terminal MS #5.
By this means, transmission rights are provided to terminals MS for one slot in the time direction and at intervals of ten subchannels in the subchannel direction. In this way, in the sixth aspect, by changing the usage region at every time slot, a guard band is inserted, and a transmission terminal can receive information for other groups in the same slot.
Patent Application
20080019315
