Ad-hoc network duplex voice long distance transmission method based on OFDM

Abstract

The application discloses a long-distance duplex voice transmission method based on OFDM in an ad hoc network, and relates to the technical field of wireless communication.The application effectively solves the contradiction between low spectral efficiency and insufficient anti-interference capability of a traditional OFDM system in low-rate voice transmission through an adaptive subcarrier allocation and parameter optimization mechanism, dynamically divides the total bandwidth into a voice-dedicated subcarrier group and a data service subcarrier group, adopts a narrower subcarrier interval for voice service to accurately match the bandwidth requirement, thereby greatly improving spectral utilization rate under the premise of ensuring voice quality, and dynamically adjusts the cyclic prefix length according to the real-time estimated maximum multipath delay of a channel to ensure that the inter-symbol interference caused by multipath can be completely eliminated, and the spectral resource waste caused by a fixed-length cyclic prefix is avoided, and the intelligent linkage of volume and riding state is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless communication, in particular to a duplex voice long-distance transmission method based on OFDM in ad hoc network. BACKGROUND

[0002] In the application scenarios of mobile ad hoc networks such as motorcycle riding communication, higher requirements are put forward for the real-time performance, communication distance, anti-interference ability and multi-device self-organizing ability of voice communication between helmet riding earphones.

[0003] At present, the existing schemes mostly use Bluetooth or private protocols based on 2.4GHz ISM frequency band. Although Bluetooth technology is popular, its point-to-point or one-to-many mode performs poorly in complex dynamic networking, has limited communication distance, and is easily disturbed in an open environment with significant multipath effect. Although devices based on Wi-Fi or improved protocols have improved in speed and distance, their protocol stack is complex, power consumption is high, and in the pure ad hoc network mode without a central node, the resource scheduling and conflict avoidance mechanism is difficult to meet the low latency requirement of voice communication.

[0004] Orthogonal frequency division multiplexing technology is widely used in 4G / 5G and Wi-Fi due to its high spectral efficiency and strong anti-multipath fading ability. However, its direct application in low-speed voice ad hoc networks faces challenges: spectral efficiency problem: the traditional OFDM system is designed for high-speed data transmission, and when only low-rate voice is transmitted, the fixed subcarrier spacing and cyclic prefix will result in low spectral efficiency; duplex and real-time problem: existing ad hoc OFDM systems often use time division multiple access or time division duplex scheme, and strict time slot allocation and switching will inevitably cause scheduling delay and switching gap, making it difficult to achieve natural and non-perceptual duplex voice interaction experience similar to a walkie-talkie.

[0005] Poor dynamic environment adaptability: the OFDM system with fixed parameters cannot effectively cope with the rapidly changing channel conditions in motorcycle riding, such as multipath delay variation and sudden same-frequency interference, resulting in unstable communication quality.

[0006] Therefore, there is an urgent need for a transmission scheme for special voice between motorcycle helmet riding earphones that can balance long distance, low latency and high anti-interference ability. SUMMARY

[0007] The duplex voice long-distance transmission method based on OFDM self-organizing network aims at solving the problems in the prior art, and can effectively solve the contradiction between low spectral efficiency and insufficient anti-interference ability of the traditional OFDM system in low-rate voice transmission through an adaptive subcarrier allocation and parameter optimization mechanism, dynamically divides the total bandwidth into a voice dedicated subcarrier group and a data service subcarrier group, adopts a narrower subcarrier spacing for the voice service to accurately match the bandwidth requirement, thereby greatly improving the spectral utilization rate under the premise of ensuring the voice quality, dynamically adjusts the cyclic prefix length according to the real-time estimated maximum multipath delay of the channel to ensure that the inter-symbol interference caused by the multipath can be completely eliminated, and the spectral resource waste caused by the fixed-length cyclic prefix is avoided, the volume and the riding state are intelligently linked, when the acceleration signal is received through the data service subcarrier group, the voice playback gain is automatically increased to offset the influence of the increased wind noise during high-speed riding, and the voice instruction is ensured to be clear.

[0008] The duplex voice long-distance transmission method based on OFDM self-organizing network aims at solving the problems in the prior art, and can effectively solve the contradiction between low spectral efficiency and insufficient anti-interference ability of the traditional OFDM system in low-rate voice transmission through an adaptive subcarrier allocation and parameter optimization mechanism, dynamically divides the total bandwidth into a voice dedicated subcarrier group and a data service subcarrier group, adopts a narrower subcarrier spacing for the voice service to accurately match the bandwidth requirement, thereby greatly improving the spectral utilization rate under the premise of ensuring the voice quality, dynamically adjusts the cyclic prefix length according to the real-time estimated maximum multipath delay of the channel to ensure that the inter-symbol interference caused by the multipath can be completely eliminated, and the spectral resource waste caused by the fixed-length cyclic prefix is avoided, the volume and the riding state are intelligently linked, when the acceleration signal is received through the data service subcarrier group, the voice playback gain is automatically increased to offset the influence of the increased wind noise during high-speed riding, and the voice instruction is ensured to be clear.

[0009] Further, in the S100, the ad hoc network protocol stack supports at least 3-hop relay forwarding; the distributed negotiation strategy is specifically: a newly added cycling wearable earphone as a new mobile terminal node, after detecting the beacon frame broadcasted by an existing mobile terminal node, performs time slot and frequency offset synchronization with the source mobile terminal node of the beacon frame, and exchanges a control packet containing its own ID and resource request to negotiate access to the communication resources in the dynamic network topology without a center, so that the network end-to-end communication delay is less than 50 ms.

[0010] Further, in the S200, the voice dedicated subcarrier group is multiplexed by frequency code joint index modulation in uplink time slots and downlink time slots; the length of the transmission frame is dynamically adjusted between 10 ms and 50 ms according to the overall channel quality; the subcarrier spacing of the voice dedicated subcarrier group is configured to support an 8 kHz audio bandwidth; and the subcarrier spacing of the data service subcarrier group is configured to support a 2 kHz bandwidth.

[0011] Further, the frequency code joint index modulation is: a first orthogonal spreading code is allocated to voice data to be transmitted by the current cycling wearable earphone as a mobile terminal node in the uplink time slot to form an uplink voice stream, a second orthogonal spreading code is allocated to voice data to be received by the current cycling wearable earphone as a mobile terminal node in the downlink time slot to correspond to a downlink voice stream, and the uplink voice stream carrying the first orthogonal spreading code and the downlink voice stream carrying the second orthogonal spreading code are multiplexed in the same voice dedicated subcarrier group to realize frequency code joint index modulation of duplex voice streams.

[0012] Further, the uplink time slot is used for the period of time when the cycling wearable earphone transmits signals to the dynamic network topology / other cycling wearable earphones; the downlink time slot is used for the period of time when the cycling wearable earphone receives signals from the dynamic network topology / other cycling wearable earphones; and the guard interval is used for an idle period of time to prevent interference between uplink and downlink time slots due to signal propagation delay.

[0013] Further, in the S300, dynamically adjusting the modulation mode of each subcarrier in the voice dedicated subcarrier group includes: maintaining a channel quality indicator value for each first subcarrier in the voice dedicated subcarrier group ; when the channel quality indicator value is higher than a first preset threshold , , selecting 16QAM modulation mode for the first subcarrier; when the channel quality indicator value is lower than the first preset threshold but higher than a second preset threshold , , selecting QPSK modulation mode for the first subcarrier; and the first preset threshold is greater than the second preset threshold, that is .

[0014] Further, in the S300, the dynamic adjustment of the cyclic prefix length of the OFDM symbol comprises: reading the allowed minimum cyclic prefix length and the maximum cyclic prefix length , wherein corresponding to a delay spread of 5μs, corresponding to a delay spread of 20μs, the maximum multipath delay of the current channel is obtained by analyzing the received pilot signal and the sampling frequency ; according to the and , the required basic cyclic prefix sampling point number is calculated, wherein is a rounding up function to ensure that the length of the cyclic prefix is sufficient to cover the maximum multipath delay; the basic cyclic prefix sampling point number is added to the preset guard length , and is constrained by the preset boundary parameter to determine the final cyclic prefix length , wherein is a function for making the cyclic prefix length ≥ , , is a function for making the cyclic prefix length ≤ ; the cyclic prefix length is configured to the OFDM modem module and applied to the generation process of the subsequent OFDM symbol to be sent.

[0015] Further, in the S400, the dynamic frequency hopping mode adopts a distributed subcarrier allocation strategy based on channel state information feedback, which is executed locally at the mobile terminal node, comprising: S401, when each cycling wearable headset is used as a mobile terminal node, the signal-to-interference-and-noise ratio of each selectable subcarrier is calculated according to the locally measured channel state information; S402, a local priority list is constructed, and all selectable subcarriers are sorted from high to low according to the signal-to-interference-and-noise ratio; S403, when allocating resources, the mobile terminal node selects the subcarrier with the highest current priority and not occupied by itself from its local priority list as a candidate subcarrier; S404, the mobile terminal node broadcasts its candidate subcarrier information on the public control channel and monitors the broadcast of other mobile terminal nodes; S405, if the same candidate subcarrier of other mobile terminal nodes is not monitored within the preset contention window, the subcarrier is occupied, otherwise, the subcarrier is removed from the local priority list and returns to S403 for reselection.

[0016] Further, in the S500, the mobile terminal node of the receiving end separates the duplex voice stream for decoding, which comprises: separating the uplink voice stream component and the downlink voice stream component from the frequency domain signal on the voice dedicated subcarrier group obtained after OFDM demodulation; using the channel state information obtained in the S300 to perform channel equalization on the separated uplink voice stream component and downlink voice stream component respectively, and performing demodulation according to the corresponding subcarrier modulation mode determined in the S300 to obtain the coded bit stream; and sending the coded bit stream obtained by demodulation into a voice decoder to restore the analog voice signal.

[0017] Compared with the prior art, the OFDM-based long-distance duplex voice transmission method for ad hoc networks has the following beneficial effects: 1. The present application effectively solves the contradiction between low spectral efficiency and insufficient anti-interference capability of traditional OFDM systems in low-rate voice transmission through adaptive subcarrier allocation and parameter optimization mechanism. The total bandwidth is dynamically divided into a voice dedicated subcarrier group and a data service subcarrier group. A narrower subcarrier spacing is used for voice services to accurately match the bandwidth requirement, thereby greatly improving the spectral efficiency while ensuring voice quality. In the face of complex and variable multipath interference in the riding environment, the cyclic prefix length of the present application is dynamically adjusted according to the real-time estimated maximum multipath delay of the channel, ensuring that the inter-symbol interference caused by multipath can be completely eliminated, and the waste of spectral resources caused by fixed-length cyclic prefix is avoided, realizing the intelligent linkage of volume and riding state. When an acceleration signal is received through the data service subcarrier group, the voice playback gain is automatically increased to offset the increased wind noise during high-speed riding, ensuring clear voice instructions.

[0018] 2. The present application combines time division duplexing and frequency division duplexing concepts and introduces frequency code joint index modulation, which fundamentally overcomes the bottleneck of high voice communication delay and the inability to realize natural full-duplex interaction in existing ad hoc networks. The voice dedicated subcarrier group is allowed to be active in the uplink and downlink time slots at the same time. By assigning different orthogonal spreading codes to the uplink and downlink voice streams, parallel transmission and separation of duplex data streams are realized at the physical layer. This duplex experience enables the riding team to hear the feedback from the tail member in real time while continuously issuing instructions, greatly improving the coordination and safety of formation riding. According to the real-time transmission of vehicle bus data, key state voice prompts or adaptive adjustment of prompt sound volume are automatically inserted in the duplex call, so that the rider can obtain the most important coordination information without being affected by the road conditions.

[0019] Other advantages, objects, and features of the present application will be apparent to those skilled in the art from the following specification, which is to be taken in conjunction with the accompanying drawings, wherein: BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0021] Figure 1 The step block diagram of the long-distance duplex voice transmission method based on OFDM ad hoc network; Figure 2 The step block diagram of the S400 in the embodiment of the present application performing the distributed dynamic frequency hopping; Figure 3 The operation flow chart of the long-distance duplex voice transmission method based on OFDM ad hoc network. DETAILED DESCRIPTION

[0022] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the accompanying drawings of the specification and specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort are within the scope of protection of the present application.

[0023] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "long-distance duplex voice transmission method based on OFDM ad hoc network", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. "Multiple" generally includes at least two.

[0024] It should also be noted that the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the goods or devices including a series of elements not only include those elements, but also include other elements not explicitly listed, or include elements inherent to such goods or devices. Without more limitations, the element defined by the sentence "including a" does not exclude the presence of other identical elements in the goods or devices including the element.

[0025] In order to improve the duplex experience and anti-interference ability of the prior art in the mobile ad hoc network voice communication of motorcycle helmet riding earphones and the like, the present application provides a long-distance transmission method for ad hoc network duplex voice based on OFDM, aiming to realize low-latency, high-reliability, full-duplex natural voice interaction in a dynamic self-organizing network by fusing time division duplex and frequency division duplex mechanisms, introducing dynamic subcarrier allocation, adaptive modulation and cyclic prefix adjustment, and frequency code joint index modulation technology. The present application is mainly applied to motorcycle formation riding, outdoor exploration cooperation, emergency command scheduling and other scenarios that require multi-node flexible networking and long-distance voice communication. In these scenarios, mobile terminal nodes need to have autonomous networking capability, support multi-hop relay, and maintain the clarity and real-time performance of voice communication under complex channel conditions such as high-speed movement, multipath interference and frequency offset changes. The present application builds a complete voice transmission system from the physical layer to the protocol stack through dynamic network topology construction, hybrid duplex frame structure design, channel state driven parameter adaptation, distributed interference avoidance and double-flow separation decoding.

[0026] Specifically, as shown in Figure 1 The long-distance transmission method for ad hoc network duplex voice based on OFDM comprises the following steps: S100, each mobile terminal node loads an ad hoc network protocol stack, broadcasts a beacon frame for network synchronization and discovery, and forms a dynamic network topology supporting relay forwarding based on a distributed negotiation strategy; S200, a transmission frame is constructed for the current transmission, the transmission frame adopts a hybrid duplex mode combining time division duplex and frequency division duplex, the transmission frame is divided into uplink time slots, downlink time slots and guard intervals in the time domain, and the total bandwidth is divided into a voice dedicated subcarrier group and a data service subcarrier group in the frequency domain; S300, each mobile terminal node obtains channel state information by receiving a pilot signal, and dynamically adjusts the modulation mode of each subcarrier in the voice dedicated subcarrier group and the cyclic prefix length of the OFDM symbol based on the channel state information; S400, each mobile terminal node identifies the interfered subcarriers based on the channel state information and avoids them through dynamic frequency hopping; S500, the mobile terminal node at the sending end sends the voice signal after mapping it to the voice dedicated subcarrier group and OFDM modulation according to the modulation mode and cyclic prefix length determined in S300, and the mobile terminal node at the receiving end performs OFDM demodulation and channel estimation on the received signal and separates the duplex voice stream for decoding.

[0027] In the implementation process, each mobile terminal node is powered on, and an embedded ad hoc network protocol stack is loaded, which supports at least 3-hop relay forwarding capability, ensuring that the voice signal can still be transmitted through intermediate nodes in a straight-line distance or in a shielding scenario, extending the communication range. After the node is started, it periodically broadcasts a beacon frame on a preset public channel, which contains node ID, timestamp, location information, remaining energy, neighbor list, etc. New nodes obtain network time reference and frequency offset information by listening to the beacon frames of existing nodes, and achieve preliminary synchronization.

[0028] The distributed negotiation strategy specifically manifests as follows: after a new node listens to the beacon frame, it sends a control message containing its own ID and resource request to the beacon source node, and the two parties negotiate the time slot and subcarrier resources required for network access through the exchange of control messages. In the negotiation process, each node preferentially selects idle resources based on local measurement of channel occupation and historical conflict records to avoid collisions. Through this distributed negotiation mechanism, the network can complete end-to-end communication link establishment within 50ms, meeting the low-latency requirements of voice communication, and the dynamic network topology formed can be updated in real time according to node movement, addition or exit, supporting multi-path relay and improving link redundancy and reliability.

[0029] After network discovery and synchronization are completed, the node constructs a transmission frame for each voice session, which adopts a hybrid duplex mode combining time division duplex and frequency division duplex, and the specific structure is as follows: time domain division: each transmission frame is divided into uplink time slots, downlink time slots and guard intervals in the time domain, the uplink time slots are used for the node to send voice to the network or other nodes, the downlink time slots are used for receiving voice from the network or other nodes, and the guard intervals are used to prevent interference between uplink and downlink time slots due to signal propagation delay. The transmission frame length can be dynamically adjusted between 10ms and 50ms according to the overall channel quality.

[0030] Frequency domain division: the total system bandwidth is dynamically divided into a voice dedicated subcarrier group and a data service subcarrier group. The voice dedicated subcarrier group adopts a narrower subcarrier spacing to accurately match the spectral characteristics of voice signals and improve spectral efficiency; the data service subcarrier group adopts a wider subcarrier spacing for transmitting low-speed data, and the two groups of subcarriers are arranged orthogonally in the frequency domain to avoid mutual interference.

[0031] The voice-specific subcarrier groups are multiplexed by frequency-code joint index modulation in uplink time slots and downlink time slots. The specific implementation manner is as follows: each mobile terminal node is allocated a unique first orthogonal spreading code when sending an uplink voice stream, which is used for spreading the uplink voice data. Meanwhile, the node is allocated a corresponding second orthogonal spreading code when receiving a downlink voice stream, which is used for distinguishing downlink voices from different sending nodes. The uplink voice stream and the downlink voice stream are frequency division multiplexed on the same voice-specific subcarrier group, and then code division distinguished by respective orthogonal codes, so as to realize parallel transmission and separation of duplex voice streams in the same frequency band. This design enables the node to receive the opposite voice in real time while sending the voice, realizes a natural full-duplex interaction experience similar to a walkie-talkie, and significantly improves the coordination efficiency and safety of the formation riding.

[0032] Before and during transmission, each mobile terminal node acquires channel state information in real time by receiving a pilot signal, such as a known pilot subcarrier inserted in an OFDM symbol, including channel gain, phase offset, signal-to-noise ratio, multipath time delay spread, etc. of each subcarrier, and dynamically adjusts the modulation mode of each subcarrier in the voice-specific subcarrier group and the cyclic prefix length of the OFDM symbol, wherein: the modulation mode of each subcarrier in the voice-specific subcarrier group is dynamically adjusted, and each subcarrier in each voice-specific subcarrier group independently maintains a channel quality indicator value , such as signal-to-noise ratio SNR or signal-to-interference noise ratio SINR, two threshold values are preset: a first preset threshold and a second preset threshold , and , the adjustment strategy is: when , indicating that the channel quality is good, 16QAM modulation mode is selected for the subcarrier to improve spectral efficiency; when , indicating that the channel quality is general, QPSK modulation mode is selected for the subcarrier to ensure transmission reliability; when , indicating that the channel quality is poor, the subcarrier is temporarily disabled or included in a frequency hopping avoidance list.

[0033] The cyclic prefix length of the OFDM symbol is dynamically adjusted, and the allowed minimum cyclic prefix length (corresponding to a time delay spread of 5 μs) and the maximum cyclic prefix length (corresponding to a time delay spread of 20 μs) are preset, the maximum multipath delay of the current channel is estimated by analyzing the received pilot signal, and the system sampling frequency , the required basic cyclic prefix sampling point number is calculated: , wherein, represents rounding up. On this basis, a preset guard length (To cope with timing error and frequency offset), and by determining the final cyclic prefix length , to ensure both completely cover multipath delay, eliminate inter-symbol interference, and not too long to cause spectrum waste. Adjusted immediately applied to the generation of subsequent OFDM symbols.

[0034] To cope with burst co-channel interference or deep fading, each node performs distributed dynamic frequency hopping based on local channel state information, as shown in Figure 2 The specific steps are as follows: S401, the node calculates the signal-to-interference-and-noise ratio of each selectable subcarrier according to the local measured channel state information; S402, construct a local priority list, sort all selectable subcarriers from high to low according to SINR;

[0035] S403, when subcarriers need to be allocated or replaced, the node selects the highest priority subcarrier that is not occupied by itself from the local list as a candidate; S404, the node broadcasts the candidate subcarrier information on the public control channel and listens to the broadcasts of other nodes; S405, if no other node claims the same subcarrier within the preset contention window, the node formally occupies the subcarrier; otherwise, remove the subcarrier from the local list and return to S403 to reselect.

[0036] This distributed strategy based on competition and priority can achieve fast and fair subcarrier allocation without central coordination, effectively avoid interference, and improve the overall anti-interference ability of the system.

[0037] At the sending end, after the voice signal is encoded (such as AMR, Opus, etc. Low bit rate speech coding), the adaptive modulation mode determined by S300 is used to map the encoded bits to the constellation points corresponding to the voice dedicated subcarrier group. Then, OFDM modulation is performed: add a dynamically adjusted cyclic prefix, perform IFFT transformation, generate a time domain signal and send it.

[0038] At the receiving end, the node synchronizes the received time domain signal, removes the cyclic prefix, performs FFT transformation to obtain the frequency domain signal, performs channel estimation and equalization through the pilot, and compensates for channel distortion. Then, the frequency domain signal on the voice dedicated subcarrier group is separated into duplex voice streams: using the first orthogonal spreading code corresponding to the uplink time slot, the signal is correlated and despread to extract the uplink voice stream component; using the second orthogonal spreading code corresponding to the downlink time slot, the signal is correlated and despread to extract the downlink voice stream component.

[0039] Two components are demodulated according to the modulation mode (16QAM or QPSK) corresponding to the subcarriers of the two components, respectively, to obtain a coded bit stream. Finally, the bit stream is sent into a voice decoder to restore an analog voice signal, which is played through a headset.

[0040] In addition, the system also supports the intelligent linkage of voice and riding state. When the node receives an acceleration signal or a high-speed identifier through the data service subcarrier group, the voice playing gain is automatically increased to offset the increased wind noise during high-speed riding, so that the voice is clear and audible. In duplex communication, the system can automatically insert a key state voice prompt or adaptively adjust the prompt sound volume according to the real-time transmission of the vehicle bus data, so that the rider can obtain the most important cooperation and safety information without feeling.

[0041] As shown in Figure 3 The specific steps of the long-distance duplex voice transmission method based on the OFDM ad hoc network provided by the application are as follows:

[0042] Each mobile terminal node loads an ad hoc network protocol stack when starting; the node periodically broadcasts a beacon frame containing its own ID, a timestamp and the like; a new node listens to the beacon frame and performs time synchronization and frequency synchronization with an existing node; the new node exchanges control messages with the beacon source node to access resources without a center; a dynamic network topology supporting at least 3-hop relaying is formed, and the end-to-end delay is controlled within 50 ms.

[0043] (2) Constructing a mixed duplex transmission frame

[0044] The transmission frame length is dynamically determined according to the current channel quality; the frame is divided into an uplink time slot, a downlink time slot and a guard interval in the time domain; the total bandwidth is divided into a voice dedicated subcarrier group and a data service subcarrier group in the frequency domain; the voice dedicated subcarrier group realizes simultaneous uplink and downlink transmission through frequency code joint index modulation.

[0045] (3) Adaptive modulation and cyclic prefix adjustment

[0046] The node receives a pilot signal to obtain channel state information of each subcarrier; a channel quality indicator value is maintained for each voice subcarrier; the modulation mode (16QAM or QPSK) is dynamically selected according to the quality indicator value and a preset threshold; the maximum multipath delay of the current channel is estimated, and the cyclic prefix length is dynamically calculated and set; it is ensured that the cyclic prefix can cover the multipath delay, while avoiding resource waste.

[0047] (4) Dynamic frequency hopping and interference avoidance

[0048] Each node calculates the signal-to-noise ratio of each subcarrier based on local CSI; constructs a local subcarrier priority list; selects a subcarrier with the highest priority and not occupied as a candidate; broadcasts the candidate subcarrier information on a common control channel; occupies the subcarrier if there is no conflict within the contention window; otherwise, reselects.

[0049] (5) Voice signal transmission and reception decoding

[0050] The sending end maps the voice signal to a voice subcarrier group according to the adaptive modulation mode; performs OFDM modulation, adds a dynamic cyclic prefix, and sends a time domain signal; the receiving end performs OFDM demodulation on the received signal, extracts a frequency domain signal; separates uplink and downlink voice stream components by using orthogonal spread codes; performs channel equalization and demodulation on each component to obtain a coded bit stream; and sends the coded bit stream into a voice decoder to restore an analog voice signal output.

[0051] To sum up, the application realizes long-distance, low-latency, high-reliability, full-duplex voice transmission in a dynamic self-organizing network through the above specific embodiments, significantly improves the communication experience and safety in motorcycle formation riding and other scenarios, and has environmental adaptability and anti-interference performance, and is suitable for complex and changeable outdoor mobile communication environments.

[0052] The above is only a preferred embodiment of the application, and does not limit the application in any form. Although the application has been disclosed as above, it is not intended to limit the application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the application, and any equivalent embodiments with equivalent changes are equivalent. Any modification, change, modification and modification of the above embodiments according to the technical essence of the application are still within the scope of the application.

Claims

1. A method for long distance transmission of duplex voice in an OFDM-based ad hoc network, characterized in that, The method is applied to a dynamic self-organizing network composed of multiple riding wearable earphones as mobile terminal nodes, and the specific steps are as follows: S100, each riding wearable earphone as a mobile terminal node loads a self-organizing network protocol stack, broadcasts a beacon frame to perform network synchronization and discovery, and forms a dynamic network topology supporting relay forwarding based on a distributed negotiation strategy; S200, a transmission frame is constructed for current transmission, the transmission frame adopts a hybrid duplex mode combining time division duplex and frequency division duplex, the transmission frame is divided into an uplink time slot, a downlink time slot and a guard interval in the time domain, and the total bandwidth is divided into a voice dedicated subcarrier group and a data service subcarrier group in the frequency domain; S300, each mobile terminal node obtains channel state information by receiving a pilot signal, and dynamically adjusts the modulation mode of each subcarrier in the voice dedicated subcarrier group and the cyclic prefix length of the OFDM symbol based on the channel state information; S400, each mobile terminal node identifies an interfered subcarrier based on the channel state information and avoids it by a dynamic frequency hopping mode; S500, the mobile terminal node of the sending end sends the voice signal after mapping the voice signal to the voice dedicated subcarrier group and performing OFDM modulation according to the modulation mode and the cyclic prefix length determined in S300, and the mobile terminal node of the receiving end performs OFDM demodulation and channel estimation on the received signal and separates and decodes the duplex voice stream.

2. The OFDM-based ad hoc network duplex voice long-range transmission method according to claim 1, characterized in that, In S100, the self-organizing network protocol stack supports at least 3-hop relay forwarding; The distributed negotiation strategy is as follows: a newly added riding wearable earphone as a new mobile terminal node synchronizes a time slot and a frequency offset with a source mobile terminal node of a beacon frame after detecting the beacon frame broadcast by the existing mobile terminal node, exchanges a control message containing an ID and a resource request, and negotiates access to the communication resources in the dynamic network topology without a center, so that the network end-to-end communication delay is less than 50 ms.

3. The OFDM-based ad hoc network duplex voice long-range transmission method according to claim 1, characterized in that, In S200, the voice dedicated subcarrier group is multiplexed by frequency code joint index modulation in the uplink time slot and the downlink time slot; The length of the transmission frame is dynamically adjusted between 10 ms and 50 ms according to the overall channel quality; The subcarrier spacing of the voice dedicated subcarrier group is configured to support an 8 kHz audio bandwidth; The subcarrier spacing of the data service subcarrier group is configured to support a 2 kHz bandwidth.

4. The OFDM-based ad hoc network duplex voice long-range transmission method according to claim 3, characterized in that, The frequency code joint index modulation is as follows: a first orthogonal spreading code is allocated to voice data to be sent by the current riding wearable earphone as a mobile terminal node in the uplink time slot to form an uplink voice stream, a second orthogonal spreading code is allocated to voice data to be received by the current riding wearable earphone as a mobile terminal node in the downlink time slot to correspond to a downlink voice stream, and the uplink voice stream carrying the first orthogonal spreading code and the downlink voice stream carrying the second orthogonal spreading code are multiplexed in the same voice dedicated subcarrier group to realize frequency code joint index modulation of the duplex voice stream.

5. The OFDM-based ad hoc network duplex voice long-range transmission method of claim 1, wherein, The uplink time slot is used for the period when the riding wearable earphone sends signals to the dynamic network topology / other riding wearable earphones. The downlink time slot is used for the period of receiving signals from dynamic network topology / other cycling wearing earphones by cycling wearing earphones; The guard interval is used for the idle period to prevent interference between uplink and downlink time slots due to signal propagation delay.

6. The OFDM-based ad hoc network duplex voice long-range transmission method of claim 1, wherein, In the S300, dynamically adjusting the modulation mode of each subcarrier in the voice dedicated subcarrier group comprises: maintaining a channel quality indicator value for a first subcarrier within each of the voice-specific subcarrier groups ; When the channel quality indicator value is higher than the first preset threshold ,Right now At that time, 16QAM modulation is selected for the first subcarrier; when the channel quality indication value is lower than the first preset threshold but higher than a second preset threshold , i.e. QPSK modulation mode is selected for the first subcarrier; When the channel quality indicator value is higher than the second preset threshold ,Right now When this happens, disable the first subcarrier; The first preset threshold is greater than the second preset threshold, that is .

7. The OFDM-based ad hoc network duplex voice long-range transmission method according to claim 1, characterized in that, In the S300, dynamically adjusting the cyclic prefix length of OFDM symbol comprises: reading the allowed minimum cyclic prefix length and the maximum cyclic prefix length wherein corresponding to a delay spread of 5 μs, corresponding to a delay spread of 20 μs, the maximum multipath delay of the current channel is obtained by analyzing the received pilot signals and the sampling frequency ; According to the above and , the required base cycle prefix sample points wherein, is a ceiling function; The base cyclic prefix sampling point number is added to a preset guard length , and is constrained by a preset boundary parameter, to determine a final cyclic prefix length , wherein, the function is used to make the cyclic prefix length ≥ , the function is used to make the cyclic prefix length ≤ ; The length of the loop prefix The configuration is assigned to the OFDM modulation and demodulation module and applied in the generation process of subsequent OFDM symbols to be transmitted.

8. The OFDM-based ad hoc network duplex voice long-range transmission method of claim 1, wherein, In the S400, the dynamic frequency hopping mode adopts a distributed subcarrier allocation strategy based on channel state information feedback, which is executed locally at the mobile terminal node, comprising: S401, when each cycling wearing earphone acts as a mobile terminal node, the signal-to-interference-and-noise ratio of each selectable subcarrier is calculated according to the locally measured channel state information; S402, a local priority list is constructed, and all selectable subcarriers are sorted from high to low according to the signal-to-interference-and-noise ratio; S403, when allocating resources, the mobile terminal node selects the subcarrier with the highest current priority and not occupied by itself from its local priority list as a candidate subcarrier; S404, the mobile terminal node broadcasts its candidate subcarrier information on the public control channel and monitors the broadcast of other mobile terminal nodes; S405, if no other mobile terminal node with the same candidate subcarrier is monitored within the preset contention window, the subcarrier is occupied, otherwise, the subcarrier is removed from the local priority list, and S403 is returned to reselect.

9. The OFDM-based ad hoc network duplex voice long-range transmission method of claim 1, wherein, In the S500, the step of the mobile terminal node of the receiving end separating and decoding the double duplex voice stream is: Separating the uplink voice stream component and the downlink voice stream component from the frequency domain signal on the voice dedicated subcarrier group obtained after OFDM demodulation; Using the channel state information obtained in S300, respectively performing channel equalization on the separated uplink voice stream component and downlink voice stream component, and demodulating according to the corresponding subcarrier modulation mode determined in S300 to obtain the coded bit stream; Sending the coded bit stream obtained by demodulation into the voice decoder to restore it to an analog voice signal.

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