Exploiting Capture Effect in Frameless ALOHA for Massive Wireless Random Access

The analogies between successive interference cancellation (SIC) in slotted ALOHA framework and iterative belief-propagation erasure-decoding, established recently, enabled the application of the erasure-coding theory and tools to design random access schemes. This approach leads to throughput substantially higher than the one offered by the traditional slotted ALOHA. In the simplest setting, SIC progresses when a successful decoding occurs for a single user transmission. In this paper we consider a more general setting of a channel with capture and explore how such physical model affects the design of the coded random access protocol. Specifically, we assess the impact of capture effect in Rayleigh fading scenario on the design of SIC-enabled slotted ALOHA schemes. We provide analytical treatment of frameless ALOHA, which is a special case of SIC-enabled ALOHA scheme. We demonstrate both through analytical and simulation results that the capture effect can be very beneficial in terms of achieved throughput.Comment: Accepted for presentation at IEEE WCNC'14 Track 2 (MAC and Cross-Layer Design

Characterization of Coded Random Access with Compressive Sensing based Multi-User Detection

The emergence of Machine-to-Machine (M2M) communication requires new Medium Access Control (MAC) schemes and physical (PHY) layer concepts to support a massive number of access requests. The concept of coded random access, introduced recently, greatly outperforms other random access methods and is inherently capable to take advantage of the capture effect from the PHY layer. Furthermore, at the PHY layer, compressive sensing based multi-user detection (CS-MUD) is a novel technique that exploits sparsity in multi-user detection to achieve a joint activity and data detection. In this paper, we combine coded random access with CS-MUD on the PHY layer and show very promising results for the resulting protocol.Comment: Submitted to Globecom 201

大規模多元接続ネットワークのためのグラフ構造に基づくランダムアクセス方式

電気通信大学201

Finite Length Analysis of Irregular Repetition Slotted ALOHA in the Waterfall Region

A finite length analysis is introduced for irregular repetition slotted ALOHA (IRSA) that enables to accurately estimate its performance in the moderate-to-high packet loss probability regime, i.e., in the so-called waterfall region. The analysis is tailored to the collision channel model, which enables mapping the description of the successive interference cancellation process onto the iterative erasure decoding of low-density parity-check codes. The analysis provides accurate estimates of the packet loss probability of IRSA in the waterfall region as demonstrated by Monte Carlo simulations.Comment: Accepted for publication in the IEEE Communications Letter

逐次干渉除去とZigZag復号に基づくランダムアクセスプロトコルの解析と設計

超多数の端末が散発的に通信するネットワークの実現のため，多元接続方式としてランダムアクセスを適用する研究が多くなされている.ランダムアクセスの一種である非正則繰り返しスロット化 ALOHA(IRSA: Irregular Repetition Slotted ALOHA)は，パケット復調の手段として逐次干渉除去を用いて高いスループット性能を達成するものの，高負荷時における性能の劣化が著しいことが知られている.そこで，本研究では逐次干渉除去に加えてジグザグ復号を組み合わせることで高負荷時におけるスループット性能の劣化を抑圧するジグザグ復号可能な符号化スロット化 ALOHA(ZDCSA: Zigzag Decodable Coded Slotted ALOHA) および拡張 ZDCSA(EZDCSA: Enhanced-ZDCSA) を提案する. 一方で，IRSA と異なり時間フレーム長が固定でないフレームレス ALOHA が提案されており，逐次干渉除去に加えてキャプチャ効果を適用した場合の性能解析がなされている.キャプチャ効果を適用する場合，基地局に到着したパケットの信号対干渉雑音電力(SINR: Signal-to-Interference-plus-Noise Ratio)は基地局に近いユーザが遠いユーザと比較して高くなり復調が容易になると予測される.従来研究では，このような幾何学的配置構造を利用したプロトコルの設計はなされておらず，ユーザ全体で時間スロットあたりのパケットの送信確率を同一としている.本研究ではユーザが自身と基地局との距離を既知であるとし，パケットの送信確率を自律的に決定する距離を考慮した非正則フレームレス ALOHA(DIFA: Distance-aware Irregular Frameless ALOHA)を提案する.本論文では，提案方式である ZDCSA，E-ZDCSA，および DIFAが既存方式と比較して優れた スループット性能を達成することを数値解析より示す.電気通信大学201

Prioritized Random MAC Optimization via Graph-based Analysis

Motivated by the analogy between successive interference cancellation and iterative belief-propagation on erasure channels, irregular repetition slotted ALOHA (IRSA) strategies have received a lot of attention in the design of medium access control protocols. The IRSA schemes have been mostly analyzed for theoretical scenarios for homogenous sources, where they are shown to substantially improve the system performance compared to classical slotted ALOHA protocols. In this work, we consider generic systems where sources in different importance classes compete for a common channel. We propose a new prioritized IRSA algorithm and derive the probability to correctly resolve collisions for data from each source class. We then make use of our theoretical analysis to formulate a new optimization problem for selecting the transmission strategies of heterogenous sources. We optimize both the replication probability per class and the source rate per class, in such a way that the overall system utility is maximized. We then propose a heuristic-based algorithm for the selection of the transmission strategy, which is built on intrinsic characteristics of the iterative decoding methods adopted for recovering from collisions. Experimental results validate the accuracy of the theoretical study and show the gain of well-chosen prioritized transmission strategies for transmission of data from heterogenous classes over shared wireless channels