Markov chain analysis of collaborative codes in random multi access communication systems

A new channel coding approach was proposed in [1] for random multiple access communication over the discrete-time memoryless channel. The coding approach allows users to choose their communication rates independently without sharing the rate information among each other or with the receiver. The receiver will either decode the message or report a collision depending on whether reliable message recovery is possible. It was shown that, asymptotically as the codeword length goes to infinity, the set of communication rates supporting reliable message recovery can be characterized by an achievable region which equals Shannon's information rate region possibly without a convex hull operation. In this paper, we derive achievable bounds on error probabilities, including the decoding error probability and the collision miss detection probability, of random multiple access systems with a finite codeword length. Achievable error exponents are obtained by taking the codeword length to infinity.

ABSTRACTThe architectural design of the Indoor Internet of Things (IIoT) network targeting static end devices (EDs) and gateways (GWs) has been innovatively formulated in this paper, integrating LoRa technology to mitigate losses and ensure seamless information reception through meticulous ED allocation. The arrangement of simultaneously transmitted data within the network server (NS) employs a deep neural network (DNN) with distributed machine learning (DML) to adjust transmission parameters, ensuring frequent uninterrupted bidirectional communication. This augmentation is obtained by strategically deploying EDs within distinct clusters determined by K‐means and density‐based spatial clustering with noise (DBSCAN), thus optimizing spreading factor (SF) and data rate (DR) allocation to prevent data congestion and improve signal‐to‐interference noise ratio (SINR). The proposed hybrid model (DR|SF) for pure and slotted ALOHA amplifies the network's performance metrics for indoor scenarios. A unified framework utilizing a one‐slope model estimates path losses (PL) while exploring various bandwidths (BW), bidirectional interrogations, and duty cycles (DC) to lower the saturation and prolong the active lifespan of the EDs. The results manifest a packet rejection rate (PRR) of 0% for the DBSCAN, contrasting a 4.7% estimate for the K‐means. The network saturation is minimized to 9.5% and 10.1%, correspondingly, significantly increasing the efficiency of slotted ALOHA (91%) and pure ALOHA (90.6%), thereby prolonging the longevity of EDs.

Multiple packet reception (MPR) is becoming a viable reality for wireless random access protocols thanks to advances in the physical layer and new coding techniques. In the simplest $K$ -MPR model, a receiver can resolve up to $K\geq 1$ parallel transmissions. We extend the classical analysis of pure and slotted ALOHA to $K$ -MPR devices with arbitrary degree $K$ for fixed and variable packet size. Through a parsimonious modeling approach, we derive relatively simple analytical expressions. In this way, we gain insight and quantitative understanding on the fundamental tradeoffs between pure and slotted ALOHA and on the scaling of maximum achievable throughput with $K$ .

We quantify the throughput capacity of wireless multi-hop networks with several medium access schemes. We analyze pure ALOHA scheme where simultaneous transmitters are dispatched according to a uniform Poisson distribution and exclusion schemes where simultaneous transmitters are dispatched according to an exclusion rule such as node coloring and carrier sense based schemes. We consider both no-fading and standard Rayleigh fading channel models. Our results show that, under no-fading, slotted ALOHA can achieve at least one-third (or half under Rayleigh fading) of the throughput capacity of node coloring scheme whereas carrier sense based scheme can achieve almost the same throughput capacity as node coloring.

The main aim of this paper is to contribute to the design of the signalling architecture for next-generation geo-satellite systems with on board processing functionality. We concentrate on the signalling channels, which are used by the satellite terminals for connection establishment. Two access methods are investigated: the dedicated and the random (Slotted Aloha) access. The dedicated access requires the introduction of a centralized scheduling technique in the network control centre. We study the system performance and demonstrate that the random access allows saving signalling bandwidth and maintaining high acceptance rate despite of collisions. This is achieved by harmonizing the random access with a centralised connection admission control algorithm and an intelligent scheduling of resource requests on board the satellite.

This paper studies distributed choice of retransmission probabilities in slotted ALOHA. Both the cooperative team problem as well as the noncooperative game problem is considered. In previous work that has focused on the maximization of throughput, it was shown that in heavy load, this maximization is obtained at the cost of a huge delay of backlogged packets. This motivates us to investigate the delay minimization problem as well as the multicriterion problem of minimizing the average expected delay (or maximizing the throughput) subject to constraints on the expected delay of backlogged packets. A Markov chain analysis is used to obtain optimal and equilibrium retransmission probabilities and expected delays analysis.

Given K simultaneously active users, an Optical CDMA (OCDMA) receiver needs to discriminate among K codes. Since the number of available codes C is always C Gt K at any given time for any truly asynchronous OCDMA system that employs quasi-orthogonal codes, there is always a set of unused codes. We here propose to exploit these unused codes to increase the spectral efficiency of the system. This can be accomplished by exclusively assigning to each user a set of M codes which represent a log2(M)-tuple of bits so that each user effectively uses a multi-dimensional modulation (multiple information bits per code are conveyed). In this paper, we analyze the performance of such a system and find in closed form an upper bound on the average probability of error. Moreover, we report for the first time that, under lightly loaded, non interference-limited conditions, the multi-dimensional OCDMA scheme here proposed allows us to obtain both higher spectral efficiency and lower bit- error probability (BEP) than a conventional OCDMA system, which employs one code only per user. The analysis here presented allow us to formulate a useful system design criterion that yields truly asynchronous OCDMA systems with very high spectral efficiency.

In cellular mobile communication systems using coded modulations, the spectrum efficiency of the system is related to the number of available codes. Recently, large area synchronous (LAS) CDMA codes, which exhibit a region called interference free window (IFW) within some delay-spread, have been accepted as one of fourth-generation (4G) wireless communication systems. However, the number of synthesized LAS codes is very low due to the low duty ratio of the sequence. In this paper, a dynamic space coded multiple access (DSCMA) scheme which utilizes the spatial diversity from smart antenna system is proposed to overcome the low spectrum efficiency in LAS CDMA system. In the DSCMA a modified version of LAS codes called LAS even ternary (LAS-ET) codes is proposed. These codes are used together with a novel algorithm called dynamic space code (DSC), which will decrease the code length so that the spectrum efficiency can be increased. By taking advantage of dynamic code reuse assignment in spatial diversity, the spectrum efficiency of the DSCMA can be further increased significantly.

Daoben Lab (DBL) access codes are generated from the Kronecker Product of the basic loose synchronization (LS) codes and a matrix. The feature is that codes are divided into several groups and the zero correlation window (ZCW) between the two different code groups is enlarged compared with the basic LS code, and the aperiodic auto-correlation and cross-correlation functions of the codes within one group are only determined by the corresponding matrix. Codes in the same group can be allocated to one user and the codes of different groups can be allocated to different users. Therefore, not only the number of available codes given the same code length is increased, but also ZCW is enlarged . Computer-based simulation also verified the feature of DBL access codes.

This paper studies the effect of multipath interference on the performance of random access techniques in which the power level of a packet depends on its time of arrival. The protocols considered are pure ALOHA and slotted ALOHA. Key performance measures such as channel throughout and mean packet delay are obtained. These results are derived partially using minislot approximation and are verified via computer simulations. For practical purposes in evaluating the successful packet reception probability the signal capture effect is also taken into consideration. How seriously the multipath interference affects the two protocols are witnessed through numerical examples. Copyright © 1999 John Wiley & Sons, Ltd.

The use of the stack protocol (also called tree protocol) to introduce a priority mechanism on the random access stage in wideband code-division multiple access (W-CDMA) seems more robust when compared with slotted ALOHA. In fact, the protocol stability in infinite population and the guaranteed low-contention delay appear very attractive for a random-access system proposal. Also, for third-generation networks, defining and offering priorities in wireless communication systems appears to be more important for operators and system users. Indeed, after voice only 2G networks, 3G systems (UMTS) should offer more services with quality and priority. However, all priorities in the UMTS system are based on the dedicated channel, which is offered after the random-access mechanism that uses the weak access protocol, slotted ALOHA. We analyze theoretically the possibility of applying the tree random-access protocol for the W-CDMA part of the UTRA radio interface proposition. We also study a priority system applied for random access directly. This seems to be very useful to propose priority for some applications, especially emergency applications. The analytical model uses generating functions and an algebraic method in order to show the stack protocol performance. Also, numerical and simulation results are presented and show the predominance of this protocol compared with the slotted-ALOHA mechanism.

Slotted Aloha and carrier sensing multiple access (CSMA) are effective random access protocols, which can also be important elements of more advanced media access protocols. In this paper, we investigate slotted Aloha and CSMA protocols in a cognitive radio network, where primary users have higher priority than secondary users and secondary users need to monitor the channel to avoid interference to the primary users, it is thus proposed that slotted Aloha is used for primary users to access the channel and secondary users use slotted CSMA to sense the time slots of slotted Aloha and transmit their packets during idle time slots. A Rayleigh fading channel is considered and we derive the throughput of slotted Aloha and CSMA for the primary and secondary users.

The general problem of allocating the capacity of a communication channel to a population of geographically distributed terminals is considered. The main locus is on the queueing problems that arise in the analysis of random access resolution algorithms. The performance measures of interest are the channel efficiency and the mean response time. The nature of known solutions for various random access schemes is discussed and a lower bound for the mean response time is conjectured.

This paper investigates variable-length feedback codes for discrete memoryless channels in point-to-point, multiple access, and random access communication. The proposed nested code employs L decoding times $n_{1}, n_{2}, \ldots, n_{L}$ for the point-to-point and multiple access channels and KL decoding times $\left\{n_{k, \ell}: 1 \leq k \leq K, 1 \leq \ell \leq L\right\}$ for the random access channel with at most K active transmitters; in the latter case, decoding times $n_{k, \ell}, 1 \leq \ell \leq L$ are reserved for decoding in the scenario where the decoder believes that the number of active transmitters is k. The code has a nested structure, i.e., codewords used to decode messages from k active transmitters are prefix of codewords used to decode messages from $k+1$ active transmitters. The code employs single-bit, scheduled feedback from the receiver to the transmitters at each potential decoding time to inform the transmitters whether or not it is able to decode. Transmitters cease transmission, thereby truncating their codewords, when no further transmissions are required by the decoder. The choice of decoding times is optimized to minimize the expected decoding time subject to an error probability constraint, and second order achievability bounds are derived.

This paper proposes a distributed energy-harvesting random access protocol called harvest-or-access by applying slotted ALOHA to wireless powered communication networks (WPCNs). From the fact that there are a considerable number of idle slots during which any nodes do not attempt transmission in slotted ALOHA, the idle slots are made available for wireless energy transfer (WET). If any random access (RA) slot is recognized as an idle slot, the hybrid access point (HAP) opportunistically performs the WET in this slot. The wireless devices (WDs) can harvest energy for every idle slot and attempt random access by using this harvested energy. An asymptotic throughput analysis in a high signal-to-noise ratio (SNR) environment with a sufficient number of accessing WDs shows that there is an optimal number of RA slots allocated to maximize throughput and this optimal number of RA slots depends only on the average of the minimum SNRs of the WDs without knowledge of full channel state information. Monte Carlo simulation results further show that the proposed harvest-or-access protocol outperforms the conventional harvest-then-transmit-based random access protocols especially when the number of WDs is large.