Space division multiplexing method based on millimeter wave directional CSMA / CA protocol

Abstract

The invention discloses a space division multiplexing method based on a millimeter wave directional CSMA / CA protocol. The space division multiplexing method is an improved method based on an IEEE802.11ad protocol. The method comprises an exhaustive beamforming training mechanism with power measurement capability and a centralized CSMA / CA space division multiplexing access mechanism. By adopting the method disclosed by the invention, the efficiency of the beam forming training and power measurement process can be improved, the problems of dehearing and terminal hiding are solved while space division multiplexing transmission under a CSMA / CA access mechanism is realized, and the system throughput is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of communication technologies, and more specifically, to a space division multiplexing method based on a millimeter wave directional CSMA / CA protocol. Background Art

[0002] 60 GHz millimeter waves have a wide frequency band of up to 7 GHz and are regarded as a key technology to meet the requirements of next-generation multi-Gbps communications. Due to the large path attenuation of 60 GHz millimeter wave signals during transmission and their susceptibility to obstruction by obstacles, the communication distance based on the 60 GHz millimeter wave band is usually short. To increase the communication distance, directional communication technologies based on beamforming are generally used. Directional antennas are used to concentrate the transmitted signals within a narrow beam and to receive signals within a narrow beam at the same time. The introduction of directional antennas reduces the interference between multiple directional links, so parallel transmission of multiple directional communication links, that is, space division multiplexing, can be achieved.

[0003] The IEEE 802.11ad protocol is the first technology to apply millimeter wave technology to Wireless Local Area Networks (WLANs). This protocol specifies the specific mechanisms for beamforming training and channel access among ordinary nodes (Stations, STAs) in a WLAN. The channel access time in the IEEE 802.11ad protocol is divided into several consecutive beacon intervals (BIs). In the Association Beamforming Training (A-BFT) phase, each STA in the WLAN performs beamforming training with the PBSS Control Point (PCP). During the Data Transmission Interval (DTI), beamforming training is performed among STAs in the WLAN, and channels are accessed to transmit data. During the Contention-based Access Period (CBAP) in the DTI, each STA uses the mechanism of Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) to compete for channel access; during the Scheduled Service Period (SP) in the DTI, each STA uses the mechanism of Time Division Multiple Access (TDMA) to access the channel without contention.

[0004] However, the beamforming training mechanism in the IEEE 802.11ad protocol only occurs between two STAs, and the remaining STAs cannot participate. Moreover, the beamforming training process is independent of the transmission power measurement process, which makes the beamforming training and power measurement processes very inefficient. At the same time, the IEEE 802.11ad protocol does not provide a spatial division multiplexing method for the CSMA / CA access mechanism and a mechanism to solve the deafness and hidden terminal problems. Therefore, it is necessary to design a high-efficiency beamforming training and power measurement mechanism based on the existing IEEE 802.11ad protocol framework, and at the same time design a spatial division multiplexing method for the CSMA / CA access mechanism to solve the deafness and hidden terminal problems while realizing spatial division multiplexing transmission. Summary of the Invention

[0005] The technical problem to be solved by the present invention is as follows: The present invention provides a spatial division multiplexing method based on a millimeter-wave directional CSMA / CA protocol, which is an improved method based on the IEEE 802.11ad protocol, improving the efficiency of the beamforming training and power measurement processes in the IEEE 802.11ad protocol, and solving the deafness and hidden terminal problems while realizing spatial division multiplexing transmission under the CSMA / CA access mechanism. Under the same number of nodes and network transmission load, the present invention can shorten the time of the beamforming training and power measurement processes and achieve a larger system throughput.

[0006] The technical solution adopted by the present invention is as follows: The present invention provides a spatial division multiplexing method based on a millimeter-wave directional CSMA / CA protocol, which mainly includes an exhaustive beamforming training mechanism with power measurement capabilities and a centralized CSMA / CA spatial division multiplexing access mechanism, and includes the following steps:

[0007] S1: During the Beacon Transmission Interval (BTI), the PCP sends a beacon frame to each sector to notify all STAs in the WLAN to execute the exhaustive beamforming training mechanism with power measurement capabilities during the subsequent A-BFT period;

[0008] S2: During the A-BFT period, all STAs execute the exhaustive beamforming training mechanism with power measurement capabilities in sequence in a TDMA manner;

[0009] S3: During the DTI period, all STAs execute the centralized CSMA / CA spatial division multiplexing access mechanism to access the channel and transmit data.

[0010] Preferably, in step S1, the PCP notifies each STA to execute the beamforming training mechanism with power measurement capabilities, specifically:

[0011] The PCP first sends a beacon frame to antenna sector 1 to notify the STAs in sector 1 to perform an exhaustive beamforming training mechanism with power measurement capabilities, and then sequentially sends beacon frames to sectors 2, 3, …, M. Here, M is the maximum sector number of the antenna. When the PCP sends the beacon frame, the remaining STAs all receive it in the omnidirectional mode. When the PCP finishes sending beacon frames to all sectors, step S1 ends.

[0012] Preferably, in step S2, each STA performs an exhaustive beamforming training mechanism with power measurement capabilities, specifically:

[0013] S2.1: Each STA sequentially sends sector sweep frames (Sector Level Sweep Frame, SSW Frame) in each sector, and the remaining STAs directionally receive the sector sweep frames in each sector while measuring the power of the received signal. Specifically: STA 1 first sends M sector sweep frames towards sector 1. At this time, the remaining STAs directionally receive the sector sweep frames one by one in M sectors and measure the received signal power; then STA 1 sends M sector sweep frames towards sector 2, and the remaining STAs receive the sector sweep frames one by one in M sectors; STA 1 will then send M sector sweep frames towards sectors 3, 4, …, M respectively, and the remaining STAs also receive the sector sweep frames one by one in M sectors; after STA 1 sends a cumulative M×M sector sweep frames towards all sectors, STA 2 will start to send sector sweep frames in sequence in each sector using the same method; after STA2 finishes sending the sector sweep frames, STA3 immediately sends the sector sweep frames until all N STAs have completed sending the sector sweep frames. Here, N is the number of STAs.

[0014] S2.2: After all STAs have completed sending the sector sweep frames, the beamforming training between all STAs has been completed. At this time, each STA will use the TDMA method to send the power measurement results to the PCP. Specifically: STA1 first sends the power measurement results towards the PCP, and then STA2 sends the power measurement results towards the PCP until all N STAs have completed sending the power measurement results.

[0015] S2.3: After the PCP receives the power measurement results sent by each STA, it will generate a power matrix for each pair of STAs. Taking transmission link i as an example, its sending STA and receiving STA are TX i and RX i , and the power matrix is:

[0016]

[0017] where R u，vIndicating TX i Sent towards sector u, RX i Received signal power when receiving towards sector v.

[0018] Preferably, in step S3, each STA executes a centralized CSMA / CA spatial division multiplexing access mechanism to access the channel for data transmission. This centralized CSMA / CA spatial division multiplexing access mechanism adopts a new handshaking mechanism, using the PCP as the central coordinator to schedule the transmission of the spatial division multiplexing link. Taking transmission link i as an example, specifically:

[0019] S3.1: TX i Send a Directional Request To Send (DRTS) towards the PCP;

[0020] S3.2: After correctly receiving the DRTS, the PCP determines whether the transmission of link i meets the spatial division multiplexing conditions and uses an adaptive response mechanism to send a response to TX i Specifically as follows:

[0021] S3.2.1: If the transmission of link i meets the spatial division multiplexing conditions, the PCP will further determine which STAs among the remaining STAs need to delay the sending of their DRTSs, and at the same time use the adaptive response mechanism to determine whether the PCP should send an omni-directional response or a directional response. Specifically:

[0022] S3.2.1.1: If the PCP can send an omni-directional response, send the PCP’s Omni-directional Clear To Send (POCTS) omni-directionally;

[0023] S3.2.1.2: If the PCP cannot send an omni-directional response, first send the PCP’s Directional Request To Send (PDRTS) directionally to RX i Then send the PCP’s Directional Allow To Send (PDATS) directionally to TX i

[0024] S3.2.2: If the transmission of link i does not meet the spatial division multiplexing conditions, the PCP sends the PCP’s Directional Reject To Send (PRJTS) directionally to TX i

[0025] S3.3: Each STA in the WLAN operates according to the response sent by the PCP received, specifically:

[0026] S3.3.1: If the PCP permits the transmission of link i, specifically:

[0027] S3.3.1.1: If the PCP sends an omni-directional reply, then the RX i aligns the antenna with the TX after receiving the POCTS i prepares to receive the Directional DATA (DDATA), and the TX i aligns the antenna with the RX after receiving the POCTS i sends the DDATA and enters step S3.4;

[0028] S3.3.1.2: If the PCP sends a directional reply, then the RX i aligns the antenna with the TX after receiving the PDRTS i prepares to receive the DDATA, and the TX i aligns the antenna with the RX after receiving the PDATS i sends the DDATA and enters step S3.4;

[0029] S3.3.2: If the PCP does not permit the transmission of link i, then the TX i enters the binary exponential backoff mode after receiving the PRJTS, waits for the backoff to end and then retransmits the DRTS, and step S3 ends;

[0030] S3.3.3: If the PCP does not correctly receive the DRTS i sent by the TX, then the PCP does not send a reply. The TX i If no reply from the PCP is received after the receiving waiting window ends, then it enters the binary exponential backoff mode, waits for the backoff to end and then retransmits the DRTS, and step S3 ends.

[0031] S3.4: The TX i sends the DDATA to the RX i and then waits for the reply i sent by the RX, specifically:

[0032] S3.4.1: If the RX i successfully receives the DDATA, then it sends a i Directional Acknowledgment (DACK) to the TX, and this transmission is successful, and step S3 ends;

[0033] S3.4.2: If the RX i does not successfully receive the DDATA, then it does not send a reply to the TX i The TX i If no reply from the RX is received after the receiving waiting window endsi If there is a reply, it enters the binary exponential backoff mode, waits for the backoff to end, and then retransmits the DRTS. This transmission fails, and step S3 ends.

[0034] Preferably, in order to further solve the deafness and hidden terminal problems, the Communicating STA Counter (CST) and the Network Allocation Vector (NAV) of the currently communicating STAs are used. The CST records the serial numbers of the currently communicating STAs and the duration of their communication; the NAV records the duration that the current STA needs to back off before sending the DRTS. Specifically: The PCP determines which STAs need to delay sending the DRTS and includes the information of these STAs that need to delay in the reply sent by the PCP; at the same time, the reply from the PCP also includes the information of the STAs that are currently performing data transmission and the transmission time; when the remaining STAs receive the PDRTS, PDATS, or POCTS sent by the PCP, they can set the CST and NAV accordingly based on the information in these replies. Before an STA sends a DRTS to the PCP, it first needs to check the CST and NAV. Taking TX i as an example, it first checks whether RX i exists in its own CST and checks whether its own NAV is 0: If RX i is not in the CST and the NAV of TX i is 0, then it can send a DRTS to the PCP; otherwise, TX i will delay sending the DRTS to the PCP.

[0035] The present invention proposes a space division multiplexing method based on a millimeter wave directional CSMA / CA protocol, which has the following beneficial effects: It proposes an exhaustive beamforming training mechanism with power measurement capabilities, combines the exhaustive beamforming training with power measurement, and enables the beamforming training and power measurement of all STAs to be completed together in one process, improving the efficiency of beamforming training and power measurement; it proposes a centralized CSMA / CA space division multiplexing access mechanism and introduces mechanisms such as adaptive reply, CST, and NAV, which not only realizes space division multiplexing transmission under the CSMA / CA access mechanism, but also solves the deafness and hidden terminal problems and improves the system throughput. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a flowchart of the space division multiplexing method based on the millimeter wave directional CSMA / CA protocol proposed by the present invention;

[0037] Figure 2 is a schematic diagram of the exhaustive beamforming training mechanism with power measurement capabilities proposed by the present invention;

[0038] Figure 3 It is a schematic diagram of frame interaction for the centralized CSMA / CA space-division multiplexing access mechanism proposed by the present invention;

[0039] Figure 4 It is a curve showing the throughput variation with network traffic load under the same conditions for the space-division multiplexing method based on the millimeter-wave directional CSMA / CA protocol proposed by the present invention and three existing millimeter-wave directional CSMA / CA protocols;

[0040] Figure 5 It is a curve showing the throughput of the space-division multiplexing method based on the millimeter-wave directional CSMA / CA protocol proposed by the present invention varying with the number of STAs and the frequency of executing the exhaustive beamforming training mechanism with power measurement capabilities. Specific implementation manners

[0041] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0042] Embodiment 1

[0043] This embodiment shows the process of the space-division multiplexing method based on the millimeter-wave directional CSMA / CA protocol proposed by the present invention, as Figure 1 shown, including the following steps:

[0044] S1: In the BTI period, the PCP sends beacon frames to each sector, notifying all STAs in the WLAN to execute the exhaustive beamforming training mechanism with power measurement capabilities in the subsequent A-BFT period;

[0045] S2: In the A-BFT period, all STAs execute the exhaustive beamforming training mechanism with power measurement capabilities in sequence in a TDMA manner;

[0046] S3: In the DTI period, all STAs execute the centralized CSMA / CA space-division multiplexing access mechanism to access the channel and transmit data.

[0047] Preferably, in step S1, when the PCP notifies each STA to execute the exhaustive beamforming training mechanism with power measurement capabilities, specifically:

[0048] The PCP first sends a beacon frame to antenna sector 1 to notify the STAs in sector 1 to execute the exhaustive beamforming training mechanism with power measurement capabilities, and then sequentially sends beacon frames to sectors 2, 3,..., M. When the PCP sends beacon frames, the remaining STAs all receive them in the omnidirectional mode. When the PCP finishes sending beacon frames to all sectors, step S1 ends.

[0049] Preferably, in step S2, each STA executes an exhaustive beamforming training mechanism with power measurement capabilities. Figure 2 It is a schematic diagram of an exhaustive beamforming training mechanism with power measurement capabilities, specifically:

[0050] S2.1: Each STA respectively sends sector scan frames in each sector in sequence, and the remaining STAs respectively receive sector scan frames directionally in each sector while measuring the power of the received signal. Specifically: STA 1 first sends M sector scan frames towards sector 1. At this time, the remaining STAs receive sector scan frames one by one in M sectors and measure the received signal power; then STA1 sends M sector scan frames towards sector 2, and the remaining STAs receive sector scan frames one by one in M sectors; STA 1 will then send M sector scan frames towards sectors 3, 4,..., M respectively, and the remaining STAs also receive sector scan frames one by one in M sectors; after STA 1 has sent a cumulative M×M sector scan frames towards all sectors, STA2 will start to send sector scan frames in each sector in sequence using the same method; after STA2 finishes sending sector scan frames, STA3 immediately sends sector scan frames until all N STAs have completed sending sector scan frames.

[0051] S2.2: After all STAs have completed sending sector scan frames, beamforming training has been completed among all STAs. At this time, each STA will use TDMA to send the power measurement results to the PCP. Specifically: STA1 first sends the power measurement results towards the PCP, and then STA2 sends the power measurement results towards the PCP until all N STAs have completed sending the power measurement results.

[0052] S2.3: After the PCP receives the power measurement results sent by each STA, it will generate a power matrix for each pair of STAs. Taking transmission link i as an example, its sending STA and receiving STA are TX i and RX i respectively, and the power matrix is:

[0053]

[0054] where P u，v represents the received signal power when TX i sends towards sector u and RX i receives towards sector v.

[0055] Preferably, in step S3, each STA executes a centralized CSMA / CA spatial division multiplexing access mechanism to access the channel and transmit data. Figure 3It is a schematic diagram of frame interaction for the centralized CSMA / CA space-division multiplexing access mechanism. This centralized CSMA / CA space-division multiplexing access mechanism adopts a new handshake mechanism and uses the PCP as the central coordinator to schedule the transmission of the space-division multiplexing link. Taking the transmission link i as an example, specifically:

[0056] S3.1: TX i Send DRTS towards the PCP;

[0057] S3.2: After correctly receiving the DRTS, the PCP determines whether the transmission of link i meets the space-division multiplexing conditions and uses the adaptive response mechanism to send a response to TX i The specific response is as follows:

[0058] S3.2.1: If the transmission of link i meets the space-division multiplexing conditions, the PCP will further determine which STAs among the remaining STAs need to delay the transmission of their DRTS, and at the same time use the adaptive response mechanism to determine whether the PCP should send an omnidirectional response or a directional response. Specifically:

[0059] S3.2.1.1: If the PCP can send an omnidirectional response, it will send POCTS omnidirectionally;

[0060] S3.2.1.2: If the PCP cannot send an omnidirectional response, it will first send PDRTS directionally to RX i and then send PDATS directionally to TX i

[0061] S3.2.2: If the transmission of link i does not meet the space-division multiplexing conditions, the PCP will send PRJTS directionally to TX i

[0062] S3.3: Each STA in the WLAN operates according to the response sent by the PCP. Specifically:

[0063] S3.3.1: If the PCP permits the transmission of link i, specifically:

[0064] S3.3.1.1: If the PCP sends an omnidirectional response, then after RX i receives the POCTS, it will align the antenna towards TX i and prepare to receive DDATA. After TX i receives the POCTS, it will align the antenna towards RX i and send DDATA, then enter step S3.4;

[0065] S3.3.1.2: If the PCP sends a directional response, then after RX i receives the PDRTS, it will align the antenna towards TX i and prepare to receive DDATA, TXi After receiving PDATS, point the antenna to RX i Send DDATA and go to step S3.4;

[0066] S3.3.2: If the PCP does not allow transmission on link i, then TX i After receiving PRJTS, it enters binary exponential backoff mode, waits for the backoff to end, and then retransmits DRTS, and step S3 ends;

[0067] S3.3.3: If the PCP does not receive TX correctly i If a DRTS is sent, the PCP will not send a reply. i If no response is received from the PCP after the receiving waiting window ends, the binary exponential backoff mode is entered, and the DRTS is retransmitted after the backoff ends, and step S3 ends.

[0068] S3.4: TX i To RX i After sending DDATA, wait for RX i The reply sent is:

[0069] S3.4.1: If RX i If DDATA is successfully received, TX i Send DACK, the transmission is successful, and step S3 ends;

[0070] S3.4.2: If RX i If DDATA is not received successfully, no signal will be sent to TX. i Send reply, TX i RX is not received after the receive wait window ends i If there is a reply, the binary exponential backoff mode is entered, and DRTS is retransmitted after the backoff ends. This transmission fails, and step S3 ends.

[0071] Preferably, in order to further solve the problems of deafness and hidden terminals, CST and NAV are used. CST records the serial number of the STA currently communicating and the duration of its communication; NAV records the duration that the current STA needs to back off before sending DRTS. Specifically: PCP determines which STAs need to delay sending DRTS, and includes the information of these STAs that need to be delayed in the reply sent by PCP; at the same time, the reply of PCP also includes the information of the STA that is currently transmitting data and the transmission time; when the remaining STAs receive the PDRTS, PDATS or POCTS sent by PCP, they can set CST and NAV accordingly according to the information in these replies. Before STA sends DRTS to PCP, it is necessary to check CST and NAV first. With TX i For example, it first checks RXi Whether it exists in its own CST and checks whether its NAV is 0: If RX i is not in the CST and TX i has a NAV of 0, then it can send DRTS to the PCP; otherwise, TX i will delay sending DRTS to the PCP.

[0072] Example 1 shows that the present invention proposes a spatial division multiplexing method based on a millimeter-wave directional CSMA / CA protocol, which has the following beneficial effects: proposes an exhaustive beamforming training mechanism with power measurement capabilities, combines the exhaustive beamforming training with power measurement, and enables the beamforming training and power measurement of all STAs to be completed together in one process, improving the efficiency of beamforming training and power measurement; proposes a centralized CSMA / CA spatial division multiplexing access mechanism, and introduces mechanisms such as adaptive response, CST, and NAV, which not only realizes spatial division multiplexing transmission under the CSMA / CA access mechanism, but also solves the deafness and hidden terminal problems, improving the system throughput.

[0073] Example 2

[0074] This example conducts a simulation experiment on the spatial division multiplexing method based on the millimeter-wave directional CSMA / CA protocol proposed by the present invention. The specific parameters are shown in Table 1.

[0075] Table 1 Simulation Parameter Table

[0076]

[0077] Preferably, the simulation scenario is set as a 10×10m 2 square area, and the simulation time is 10 beacon intervals. All STAs in the WLAN can randomly communicate with any one STA, and the process of data packets arriving at each STA follows a Poisson process. Considering the arrival rate of data packets is μ, then the network traffic load T is where D is the size of the data packet and R is the transmission rate when transmitting the data packet.

[0078] Figure 4 is the curve of the throughput varying with the network traffic load under the same conditions of the spatial division multiplexing method based on the millimeter-wave directional CSMA / CA protocol proposed by the present invention and the existing 3 millimeter-wave directional CSMA / CA protocols. It can be seen from the figure that under the same conditions, the spatial division multiplexing method based on the millimeter-wave directional CSMA / CA protocol proposed by the present invention can achieve a higher system throughput.

[0079] Preferably, it is assumed that the exhaustive beamforming training mechanism with power measurement capabilities proposed by the present invention is executed every K beacon intervals.Figure 5 It is a curve showing the variation of the throughput of the spatial division multiplexing method based on the millimeter-wave directional CSMA / CA protocol proposed by the present invention with the number N of STAs and the frequency K of performing an exhaustive beamforming training mechanism with power measurement capabilities. It can be seen from the figure that, with the same N, the throughput increases as K increases; when K = 1, the throughput first increases and then decreases as N increases; when K = 10, the throughput first increases and then remains unchanged as N increases.

[0080] Example 2 shows that, compared with the existing millimeter-wave directional CSMA / CA protocol, the spatial division multiplexing method based on the millimeter-wave directional CSMA / CA protocol proposed by the present invention can achieve more efficient beamforming training and power measurement, and can achieve higher system throughput, solving the deafness and hidden terminal problems.

Claims

1. A space division multiplexing method based on millimeter wave directional CSMA / CA protocol, characterized in that: The following steps are involved: (1) During the BTI period, the PCP sends a beacon frame to each sector, notifying all STAs in the WLAN to perform an exhaustive beamforming training mechanism with power measurement capability in the following A-BFT period; (2) During the A-BFT period, all STAs sequentially execute the exhaustive beamforming training mechanism with power measurement capability in a TDMA manner; (3) During the DTI period, all STAs implement the centralized CSMA / CA space division multiplexing access mechanism and access the channel to transmit data.

2. The space division multiplexing method based on the millimeter wave directional CSMA / CA protocol according to claim 1, characterized in that: The step (1) is specifically: The PCP sends beacon frames in a direction toward the corresponding sectors in the order of antenna sectors 1, 2, ..., M, to notify the STAs in the WLAN to perform an exhaustive beamforming training mechanism with interference measurement capability in the next A-BFT period; When the PCP sends a beacon frame, the other STAs all use the omni-directional mode to receive it.

3. The space division multiplexing method based on the millimeter wave directional CSMA / CA protocol according to claim 1, characterized in that: The step (2) is specifically: (1) Each STA uses TDMA to send sector scan frames in each sector, and the other STAs receive sector scan frames in each sector and measure the received signal power to complete beamforming training and power measurement. Each STA needs to send M beacon frames in each sector in the order of 1, 2, ..., M antenna sectors. That is, each STA needs to send M × M beacon frames in total. (2) After all STAs have completed the transmission of the sector scan frame, each STA uses TDMA to send the power measurement result to the PCP in the order of STA number 1, 2, ..., M; (3) After receiving the power measurement results sent by each STA, the PCP generates a power matrix for each pair of STAs. Taking transmission link i as an example, its transmitting STA and receiving STA are TX i and RX i , the power matrix is: Among them, P u，v Indicates TX i Sending towards sector u, RX i Received signal power when receiving towards sector v.

4. The space division multiplexing method based on the millimeter wave directional CSMA / CA protocol according to claim 1, characterized in that: Taking transmission link i as an example, step (3) is specifically as follows: (1)TX i Send DRTS towards PCP; (2) After receiving DRTS correctly, PCP first determines whether the transmission of link i meets the space division multiplexing conditions, and then uses the adaptive reply mechanism to send a reply to TX. i Send a reply, specifically: if the transmission of link i meets the conditions of space division multiplexing and can use omnidirectional reply, the PCP sends POCTS omnidirectionally; if the transmission of link i meets the conditions of space division multiplexing and cannot use omnidirectional reply, the PCP first sends POCTS to RX i Send PDRTS to TX i Directed transmission of PDATS; if the transmission of link i does not meet the conditions for space division multiplexing, the PCP sends PDATS to TX i Directed sending of PRJTS; (3) Each STA operates according to the reply sent by the PCP. Specifically, if the PCP sends POCTS, then RX i After receiving POCTS, point the antenna to TX i Prepare to receive DDATA, TX i After receiving POCTS, point the antenna to RX i Send DDATA; If PCP sends PDRTS and PDATS, RX i After receiving PDRTS, point the antenna to TX i Prepare to receive DDATA, TX i After receiving PDATS, point the antenna to TX i Send DDATA; If PCP sends PRJTS, TX i After receiving PRJTS, it enters binary exponential backoff mode and waits for the backoff to end before retransmitting DRTS. If the PCP does not send a reply, it indicates that it has failed to successfully receive TX. i DRTS sent, TX i If no response is received from PCP after the receiving waiting window ends, the system enters binary exponential backoff mode and waits for the backoff to end before retransmitting DRTS. (4)TX i To TX i After sending DDATA, wait for RX i The reply sent is: If RX i If DDATA is successfully received, TX i Send DACK, the transmission is successful; if RX i If DDATA is not received successfully, no signal will be sent to TX. i Send reply, TX i No RX received after the receive wait window has ended i If the reply is received, it will enter the binary exponential backoff mode and wait for the backoff to end before retransmitting DRTS. This transmission fails. (5) To further solve the deaf and hidden terminal problems, CST and NAV are used. When a STA receives a PDRTS, PDATS, or POCTS, it will parse the content and update the CST and NAV accordingly. Before sending a DRTS to the PCP, the STA needs to check the CST and NAV to ensure that the TX i For example: TX i First check RX i Whether it exists in its own CST, and check whether its own NAV is 0. If RX i Not in CST and TX i If the NAV is 0, DRTS can be sent to PCP, otherwise TX i Sending DRTS to PCP will be delayed.

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