New strategies for collision resolution of multi-access channel

The truncated binary exponential back-off algorithm is one of the most effective methods applied in collision resolution process of random multi-access channel.In this study,two new strategies are presented to improve the capability of the truncated binary exponential back-off algorithm.In the new strategies,the sizes of the initial window size or the operating window sizes are adjusted dynamically,which always bring a significant improvement for the self-adaptability of the original algorithm.A series of experiments are simulated and the results verify that the new strategies can make the implementation more stable and effective than the original algorithm.

An Achievable Rate Region for the Asynchronous Multiple Access Channel with Feedback

An achievable rate region for the asynchronous multiple access channel with feedback is established through the use of superposition coding, list decoding and time sharing. The calculation results demonstrate that lack of synchronization does not affect the achievable rate region when the code block length tends to infinity, and that if the length of the code word is finite, especially not sufficiently larger than a fixed maximal delay, the asynchronization will cause a loss of the rate region. The amount of such a loss with its explanation for the reason is given, and the difference between the losses for the asynchronous multiple access channel with and without feedback is also discussed in this paper.

Cooperative multiple access channels: Achievable rates and optimal resource allocation

We investigate the multiple access channels （MAC） where sources can cooperate via half-duplex relaying and refer to it as cooperative MAC channels （CMAC）. Assuming perfect channel state information （CSI） at the transmitters and the receivers, we determine the bounds on the achievable rate region of a Gaussian CMAC channel and an inner bound on the outage capacity region of a fading CMAC channel. Based on superposition modulation, a half-duplex cooperative relay scheme with optimal resource allocation is proposed to achieve the bounds of capacity region. Analytical results and simulation results show that the achievable rate region of a Gaussian CMAC channel is larger than that of a Gaussian MAC channel with direct transmission （DT） schemes. But they have the same achievable sum rate. Moreover, the proposed scheme can provide higher outage capacity region than DT schemes in a fading MAC channel due to the fact that sources can share the resources with each other to reduce outages.

A Deep Reinforcement Learning-Based Technique for Optimal Power Allocation in Multiple Access Communications

Formany years,researchers have explored power allocation(PA)algorithms driven bymodels in wireless networks where multiple-user communications with interference are present.Nowadays,data-driven machine learning methods have become quite popular in analyzing wireless communication systems,which among them deep reinforcement learning(DRL)has a significant role in solving optimization issues under certain constraints.To this purpose,in this paper,we investigate the PA problem in a k-user multiple access channels(MAC),where k transmitters(e.g.,mobile users)aim to send an independent message to a common receiver(e.g.,base station)through wireless channels.To this end,we first train the deep Q network(DQN)with a deep Q learning(DQL)algorithm over the simulation environment,utilizing offline learning.Then,the DQN will be used with the real data in the online training method for the PA issue by maximizing the sumrate subjected to the source power.Finally,the simulation results indicate that our proposedDQNmethod provides better performance in terms of the sumrate compared with the available DQL training approaches such as fractional programming(FP)and weighted minimum mean squared error(WMMSE).Additionally,by considering different user densities,we show that our proposed DQN outperforms benchmark algorithms,thereby,a good generalization ability is verified over wireless multi-user communication systems.

Hybrid Channel Access Mechanism Based on Coexistence Scenario of NR-Unlicensed

With the rapid development of 5G NR(New Radio),the explosive increment of traffic amount is calling the utilization of unlicensed band.3GPP has proposed LAA(Licensed Assisted Access)to use LTE in unlicensed band and pointed out that NR-U(NR-Unlicensed)can reuse most designs of it.However,the existing channel access mechanism of LAA is conservative under the coexistence scenario of NR-U,which leads to the waste of time resource.To address the problem this paper proposes a hybrid channel access mechanism to take advantage of the LBT(Listen-Before-Talk)mechanism of LAA when channel is quite busy and transmit directly with reduced power when it is relatively idle.The channel busy degree is judged by a series of periodically updated adaptive thresholds.System-level simulation verifies that under the coexistence scenario of NR-U the proposed mechanism can achieve higher UPT(User Perceived Throughput)and lower delay than other channel access mechanisms.

Cross-Layer Framework for Fine-Grained Channel Access in Next Generation High-Density Wi Fi Networks

Densely deployed Wi Fi networks will play a crucial role in providing the capacity for next generation mobile internet. However, due to increasing interference, overlapped channels in Wi Fi networks and throughput efficiency degradation, densely deployed Wi Fi networks is not a guarantee to obtain higher throughput. An emergent challenge is how to effi ciently utilize scarce spectrum resources, by matching physical layer resources to traffi c demand. In this aspect, access control allocation strategies play a pivotal role but remain too coarse-grained. As a solution, this research proposes a flexible framework for fine-grained channel width adaptation and multi-channel access in Wi Fi networks. This approach, named SFCA(Subcarrier Fine-grained Channel Access), adopts DOFDM(Discontinuous Orthogonal Frequency Division Multiplexing) at the PHY layer. It allocates the frequency resource with a subcarrier granularity, which facilitates the channel width adaptation for multi-channel access and thus brings more fl exibility and higher frequency efficiency. The MAC layer uses a frequencytime domain backoff scheme, which combines the popular time-domain BEB scheme with a frequency-domain backoff to decrease access collision, resulting in higher access probability for the contending nodes. SFCA is compared with FICA(an established access scheme)showing significant outperformance. Finally we present results for next generation 802.11 ac Wi Fi networks.

Web services interface to EPICS channel access

Web services is used in Experimental Physics and Industrial Control System (EPICS).Combined with EPICS Channel Access protocol,Web services' high usability,platform independence and language independence can be used to design a fully transparent and uniform software interface layer,which helps us complete channel data acquisition,modification and monitoring functions.This software interface layer,a cross-platform of cross-language, has good interopcrability and reusability.

Designing cost-effective network-on-chip by dual-channel access mechanism

A dual-channel access mechanism to overcome the drawback of traditional single-channel access mechanism for network-on-chip （NoC） is proposed. In traditional single-channel access mechanism, every Internet protocol （IP） has only one chan- nel to access the on-chip network. When the network is relatively idle, the injection rate is too small to make good use of the network resource. When the network is relatively busy, the ejection rate is so small that the packets in the network cannot leave immediately, and thus the probability of congestion is increased. In the dual-channel access mechanism, the injection rate of IP and the ejection rate of the network are increased by using two optional channels in network interface （NI） and local port of routers. Therefore, the communication performance is improved. Experimental results show that compared with traditional single-channel access mechanism, the proposed scheme greatly increases the throughput and cuts down the average latency with reasonable area increase.

Channel Estimation for Full-Duplex Relay Transmission in Cloud Radio Access Networks

Relay in full-duplex(FD) mode can achieve higher spectrum efficiency than that in half-duplex mode,while it is crucial to suppress relay self-interference to ensure transmission quality which requires instantaneous channel state information(CSI). In this paper,the channel estimation issue in FD amplify-andforward relay networks is considered,where the training-based estimation technique is adopted. Firstly,the least square(LS) estimation is implemented to obtain composite channel coefficients of source-relay-destination(SRD) channel and relay loop-interference(LI) channel in order to assist destination in performing data detection. Secondly,both LS and maximum likelihood estimation methods are utilized to perform individual channel estimation aiming at supporting successive interference cancelation at destination. Finally,simulation results demonstrate the effectiveness of both composite and individual channel estimation,and the presented ML method can achieve lower MSEs than LS solution.

MULTI-CHANNEL TRANSMISSION STRATEGY FOR DYNAMIC SPECTRUM ACCESS

Cognitive radio is a promising technology that deals with the scarcity of radio spectrum. In this paper, we propose a new multi-channel transmission strategy for dynamic spectrum access in cognitive radio network. Starting with the model of spectrum activities, we present the multi-channel transmission strategy which has primary user's protection mechanism to improve the spectrum efficiency and study its performance under perfect and imperfect sensing. Numerical example results reveal that the performance of the proposed strategy has the superiority with respect to capacity performance of cognitive users and the protection of primary users.

Network-Load Aware Adaptive Channel Access Control for WLAN

Wireless local area network (WLAN) brings us a low cost and high bandwidth experience and thus plays a critically important role in current/future networks to support high-rate transmissions. To better provide quality-of-service (QoS) for WLAN users, we in this paper propose an improved scheme called “A-EDCA”(adaptive EDCA), based on enhanced distributed channel access (EDCA) of IEEE 802.11e under the infrastructure mode. Our proposed scheme aims at efficiently adapting the transmission over WLAN to the time-varying network conditions and mitigating the competition ability unfairness between access point (AP) and non-AP stations (STAs). Specifically, all non-AP STAs adaptive-ly modify the contention window based on the network condition. Moreover, AP skips the backoff phase by setting its backoff counter as zero when non-AP STA completes transmission successfully to relieve the unfairness. At last, simulation results demonstrate the effectiveness of the proposed approach.

Joint Design of Coalition Formation and Semi-Blind Channel Estimation in Fog Radio Access Networks

Coordinated signal processing can obtain a huge transmission gain for Fog Radio Access Networks(F-RANs).However,integrating into large scale,it will lead to high computation complexity in channel estimation and spectral efficiency loss in transmission performance.Thus,a joint cluster formation and channel estimation scheme is proposed in this paper.Considering research remote radio heads(RRHs)centred serving scheme,a coalition game is formulated in order to maximize the spectral efficiency of cooperative RRHs under the conditions of balancing the data rate and the cost of channel estimation.As the cost influences to the necessary consumption of training length and estimation error.Particularly,an iterative semi-blind channel estimation and symbol detection approach is designed by expectation maximization algorithm,where the channel estimation process is initialized by subspace method with lower pilot length.Finally,the simulation results show that a stable cluster formation is established by our proposed coalition game method and it outperforms compared with full coordinated schemes.

基于空中计算CoMAC架构的不同计算场景叠加符号判决算法

本文研究不同场景下基于空中计算的多址信道计算(CoMAC)架构的覆盖符号决策算法。首先,从理论上分析了XOR、ADD、MOD三种场景中加性高斯白噪声(AWGN)多址接入信道下叠加符号的概率密度分布,提出了一种基于先验概率的最优门限判决策略。其次,推导了系统最优门限及对应误码率的理论表达式。最后,通过仿真验证了不同信噪比、传感器节点个数及先验概率对于该门限判决方案的鲁棒性和可靠性的影响。与通信计算相分离的传统方案相比,空中计算判决方案具有更好的检测性能,为多址接入信道下的信号识别提供了新的参考方案。

Network coding with diversity and outdated channel state information

Physical-layer network coding （PNC） has the potential to significantly improve the throughput of wireless networks where the channels can be modeled as additive white Gaussian noise （AWGN） channel. As extending to mul- tiple channels, this technique requires both amplitude and phase compensation at each transmitter and will lead to inef- ficient systems yielding no diversity even with perfect channel state information （CSI）. In order to avoid these limita- tions, we apply network coding with diversity （NCD） to achieve a form of selection diversity and extend NCD to coop- erative multiple access channels in this paper. However, in practical wireless communication systems, the CSI could become outdated due to the difference between the CSI used in the relay selection and data transmission phases. Hence, the selected relay may not be the best one during data transmission phase due to the dynamic change in the wireless channels. Therefore, we first explore the relation between the present and past CSIs. Exploiting this relationship, the NCD scheme with outdated CSI is investigated based on the past CSI. To evaluate the performance of this scheme, an information-theoretic metric, namely the outage capacity, is studied under this condition.

DESIGN AND PERFORMANCE OF SYMBOL/SEQUENCE TCM FOR DS/SSMA SYSTEM OVER MOBILE RADIO CHANNEL

A novel kind of multidimension symbol/sequence trellis coded modulation (TCM) based on TCM of lower coding rate has been constructed. The redundancy of this new kind of TCM is provided not only by the modulated symbol sequence but also by the PN sequences for spreading spectrum as well. The performance of direct sequence spread spectrum multiple access (DS/SSMA) system with this symbol/sequence TCM over flat Rayleigh fading channel has been investigated by theoretical analysis and numerical simulation. The results obtained in this research demonstrate the performance improvements of this system in comparison with that of the DS/SSMA system with conventional TCM under the same conditions.

Equivalent Time-Domain Representation and Uplink Channel Estimator for Multicarrier CDMA Systems

Many blind channel estimation methods have been proposed for direct sequence (DS) code-division multiple access (CDMA) systems, so we can certainly use them to estimate the finite impulse response (FIR) channel for the multi-carrier (MC-) CDMA system. In this paper, the MC-CDMA system is interpreted as an equivalent time-domain DS-CD-MA system with specific spreading codes. Then, an equivalently time-domain blind channel estimator is derived for the uplink MC-CDMA, which is based on second-order statistics of the received data. By exploiting singular value decomposition (SVD) and the finite alphabet property of transmitted symbols, the time-domain channel impulse response (CIR) for the uplink MC-CDMA can be accurately identified. Computer simulations illustrate both the validity and the overall performance of the proposed estimator.

A Media Access Control Scheme for Service Differentiation in Ad hoc Networks

IEEE 802.11 distributed coordination function(DCF)can alleviate the collision and hidden station problem,but it doesn't differentiate traffic categories(TC).Therefore,it can't provide sufficient quality of service(QoS)support for different TC.Recently,a new contention-based enhanced distributed channel access(EDCA)scheme is proposed which provides a probabilistic QoS support.In this paper,an improved EDCA scheme for service differentiation in ad hoc networks is proposed.In this scheme,signal channel resistance coefficient is used to adjust the contention window(CW).It proves that the scheme provides the traffic differentiation,high throughput and low delay through simulation.

MAC Sub-Layer Analysis with Channel Estimation in Broadband Power Line Communication

Broadband power line communication (BPLC) gained a lot of interest because of low cost and high performance communication network in access area. In this paper physical (PHY) layer and medium access control (MAC) sub-layer of BPLC are considered. Furthermore, effects of bit error rate (BER) are analyzed in MAC sub-layer. Powerful turbo convolutional code (TCC) and wideband orthogonal frequency division multiplexing (OFDM) are used in PHY layer. Carrier sense multiple access (CSMA) and virtual slot multiple access (VSMA) are taken into consideration in MAC sub-layer. Multilayered perceptrons neural network with backpropagation (BP) learning channel estimator algorithm compare to classic algorithm in for channel estimating. The simulation results show that the proposed neural network estimation decreases bit error rate then in MAC sub-layer throughput increases and access delay is decreased.

Statistical-mechanical analysis of multiuser channel capacity with imperfect channel state information

In this paper, the effect of imperfect channel state information at the receiver, which is caused by noise and other interference, on the multi-access channel capacity is analysed through a statistical-mechanical approach. Replica analyses focus on analytically studying how the minimum mean square error （MMSE） channel estimation error appears in a multiuser channel capacity formula. And the relevant mathematical expressions are derived. At the same time, numerical simulation results are demonstrated to validate the Replica analyses. The simulation results show how the system parameters, such as channel estimation error, system load and signal-to-noise ratio, affect the channel capacity.