Network-assisted Diversity Multiple Access Research Articles

Non-Blocking Scheme for Blind Network-Assisted Diversity Multiple Access in Synchronous Channels

We design a Blind Network-Assisted Diversity Multiple Access (BNDMA) method for resolving packet collisions in synchronous packet-switched networks. As opposed to typical BNDMA schemes, the method operates in non-blocking mode. Idle transmitters at the start of a collision resolution interval may join the set of active transmitters and contact the receiver before the end of the interval. A naive queuing analysis of the proposed scheme is exponentially complex in the size of the network. We carry out a computationally efficient analysis of the network throughput and queuing delay. We show that the suggested scheme reduces the queuing delay of the buffered packets at the transmitters without sacrificing the maximum throughput achieved by standard BNDMA. Further insights are derived from the numerical experiments.

Performance analysis of feedback-free collision resolution NDMA protocol

To support communications of a large number of deployed devices while guaranteeing limited signaling load, low energy consumption, and high reliability, future cellular systems require efficient random access protocols. However, how to address the collision resolution at the receiver is still the main bottleneck of these protocols. The network-assisted diversity multiple access (NDMA) protocol solves the issue and attains the highest potential throughput at the cost of keeping devices active to acquire feedback and repeating transmissions until successful decoding. In contrast, another potential approach is the feedback-free NDMA (FF-NDMA) protocol, in which devices do repeat packets in a pre-defined number of consecutive time slots without waiting for feedback associated with repetitions. Here, we investigate the FF-NDMA protocol from a cellular network perspective in order to elucidate under what circumstances this scheme is more energy efficient than NDMA. We characterize analytically the FF-NDMA protocol along with the multipacket reception model and a finite Markov chain. Analytic expressions for throughput, delay, capture probability, energy, and energy efficiency are derived. Then, clues for system design are established according to the different trade-offs studied. Simulation results show that FF-NDMA is more energy efficient than classical NDMA and HARQ-NDMA at low signal-to-noise ratio (SNR) and at medium SNR when the load increases.

A Blind Collision Resolution Protocol Based on Cooperative Transmission

Network-assisted diversity multiple access (NDMA) was recently proposed to resolve collision. The blind NDMA method using independent component analysis (ICA) ICA-NDMA, has been developed to overcome the difficulties of synchronization and orthogonal identification codes required by the training-based NDMA protocols. In this paper, we propose a novel blind collision resolution protocol, named as ICA-CoopNDMA, by employing cooperative transmission in ICA-NDMA. When K-node collision happened, a cooperative transmission mechanism is adopted to collect different mixtures of the K original packets in the following slots. After that, the destination can recover the original packets using ICA. This protocol offers spatial diversity by using relay nodes and is robust to the wireless channel. In order to determine the collision multiplicity K, a cooperative blind detection algorithm is also proposed based on minimum description length (MDL) criterion. This algorithm saves one detection slot compared with conventional MDL-based method used by ICA-NDMA. Hence, the delay of ICA-CoopNDMA is reduced. Simulation and theoretical analysis results show that, the proposed protocol can work effectively under both fast and slow fading channels. Compared with ICA-NDMA, the maximum stable throughput and average packet delay are obviously better, and the energy efficiency is higher under heavy traffic load.

Frequency-domain multipacket detection: a high throughput technique for SC-FDE systems

The traditional approach to cope with collisions is to discard the packets involved in it and to ask for their retransmission. However, since the signal associated to a collision has important information concerning the packets involved, we can efficiently resolve collisions with proper retransmissions. In this paper we consider severely time-dispersive channels and we propose a technique that allows efficient packet separation. We employ SC-FDE schemes (single-carrier with frequency-domain equalization) and we propose an iterative frequency-domain multi-packet detection. Since our technique requires uncorrelated channels for different retransmissions, we also propose an SP technique (Shifted Packets) for retransmissions in fixed channels. Since the total number of transmissions is equal to the number of packets involved in the collision (even when the channel remains fixed for the retransmissions), our technique allows high throughputs. The analysis of our detection technique combined with the NMDA (network-assisted diversity multiple access) MAC (medium access control) protocol shows significant throughput and delay improvements for low E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> values compared to a TDMA (time division multiple access) approach, where collisions are avoided. This technique is particularly appealing for the uplink of broadband wireless systems, since we consider SC-FDE schemes and the complexity is concentrated in the receiver. By employing the SP scheme we can use the same channel for the retransmissions, with only a small performance degradation.

Space and network diversity combination for masked node collision resolution in wireless ad hoc network

In wireless ad hoc networks, the traditional carrier sensing multiple access/collision avoidance protocol cannot solve the masked node problem, which affects the network performance greatly. Our proposed collision separation technique overcomes the shortcoming of the IEEE 802.11 request-to-send-clear-to-send handshake by combining the space diversity provided by the antenna array and network diversity provided by the medium access control layer. In this work, the colliding packets caused by masked nodes are not discarded but stored and combined with the selected retransmission packets to separate the data from different nodes. The steady states of the nodes in the network are analyzed via a Markov chain model. The network throughput and delay performance are also investigated. Compared to network assisted diversity multiple access, our proposed method can provide significantly higher throughput and lower delay

Wireless access with blind collision-multiplicity detection and retransmission diversity for quasi-static channels

Wireless multiple-access protocols using retransmission diversity resolve packet collisions through source separation techniques. Retransmissions are applied to achieve the necessary diversity level to determine the collision multiplicity blindly, whose proper detection is essential for good resolution performance. The so-called network-assisted diversity multiple access (NDMA) employs the rank test (RT) method for blind multiplicity detection, but static channel parameters throughout the retransmissions and the tight control of the transmitter phase are required. In this paper, a superior blind collision multiplicity-detection technique is introduced by combining the minimum description length criterion and a variation of the RT method. Collision resolution is accomplished through independent component analysis (ICA). Unlike blind NDMA,the new protocol, named ICA-NDMA, works in quasi-static fading channels, and does not need any phase control. Extensive performance analyses corroborate the performance advantages offered by ICA-NDMA.

Wireless networks with retransmission diversity access mechanisms: stable throughput and delay properties

Building on the concept of retransmission diversity, a class of collision resolution protocols, NDMA (network-assisted diversity multiple access) and BNDMA (blind NDMA), has been introduced recently for wireless packet multiple access. These protocols provide the means for improved performance compared with random access and splitting-based collision resolution protocols at a moderate receiver complexity cost. However, stability of these protocols has not been established, and the available steady-state analysis is restricted to symmetric (common-rate) systems. The stability region of (B)NDMA is formally analyzed. The tools used in the analysis range from a preliminary dominant system approach to the Foster-Lyapunov recurrence criterion and the (/spl sigma/, /spl rho/) deterministic fluid arrivals approach. It is rigorously established that the maximum stable throughput is close to 1. This is followed by a simpler and more general steady-state analysis, bypassing the earlier generating function approach, using instead only balance equations. This approach allows dealing with asymmetry (multirate systems), yielding expressions for throughput and delay per queue. Finally, we generalize BNDMA and the associated analysis to multicode systems.

Network-assisted diversity multiple access in dispersive channels

Network-assisted diversity multiple access (NDMA) is a novel random medium access method, which provides impressive throughput efficiency for multiplexing variable-bit-rate data sources. We study the implementation of the NDMA scheme in the presence of multipath channels. A transceiver architecture and random access strategies are proposed, which are able to detect and resolve collisions in the presence of unknown propagation channels. The performance issues are studied both analytically and numerically.