Takatoshi Sugiyama

Wireless network coding in slotted aloha with two-hop unbalanced traffic

This paper deals with two representative unbalanced traffic cases for two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement with multiple unicast and multisource multicast networks. We have analyzed the performance of network coding on a two-hop wireless relay access system employing the slotted ALOHA under a balanced bidirectional traffic. The relay nodes will generally undergo this unbalanced multidirectional traffic but the impact of this unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop unbalanced bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial to maximizing the achievable throughput of wireless network coding in slotted ALOHA on two-hop unbalanced traffic cases. Furthermore, we show that the throughput is enhanced even if the traffic at the relay node is unbalanced.

Throughput Analysis of Two-Hop Wireless CSMA Network Coding

This paper considers two-hop wireless systems employing network coding and a carrier sense multiple access (CSMA) protocol. Network coding is a recent and highly regarded technology for the capacity enhancement of multiple unicast and multisource multicast networks. The two-hop wireless CSMA systems are often involved with the hidden node problem, but the impact of the hidden nodes on network coding has not been analyzed in theory. This paper provides explicit expressions of the throughput for single-relay two-hop wireless CSMA systems both without and with network coding. The throughput can be obtained from these expressions for given system parameters even when end nodes via the relay node are hidden each other. Furthermore it is shown that the transmit probability of the relay node is a design parameter that is crucial for maximizing the achievable throughput for CSMA systems with network coding. It is clarified that the throughput for CSMA systems can be enhanced as compared with that for slotted ALOHA systems in case of non-hidden end nodes whereas it deteriorates considerably in case of hidden end nodes.

Performance analysis of slotted ALOHA and network coding for single-relay multi-user wireless networks

Deployment of wireless relay nodes can enhance system capacity, extend wireless service coverage, and reduce energy consumption in wireless networks. Network coding enables us to mix two or more packets into a single coded packet at relay nodes and improve performances in wireless relay networks. In this paper, we succeed in developing analytical models of the throughput and delay on slotted ALOHA (S-ALOHA) and S-ALOHA with network coding (S-ALOHA/NC) for single-relay multi-user wireless networks with bidirectional data flows. The analytical models involve effects of queue saturation and unsaturation at the relay node. The throughput and delay for each user node can be extracted from the total throughput and delay by using the analytical models. One can formulate various optimization problems on traffic control in order to maximize the throughput, minimize the delay, or achieve fairness of the throughput or the delay. In particular, we clarify that the total throughput is enhanced in the S-ALOHA/NC protocol on condition that the transmission probability at the relay node is set at the value on the boundary between queue saturation and unsaturation. Our analysis provides achievable regions in throughput on two directional data flows at the relay node for both the S-ALOHA and S-ALOHA/NC protocols. As a result, we show that the achievable region in throughput can be enhanced by using network coding and traffic control.

New throughput analysis of long-distance IEEE 802.11 wireless communication system for smart grid

The use of wireless access networks, particularly IEEE 802.11 wireless access networks, is an economical method for realizing a communication network between a core information network of a smart grid and a rural area network. This paper presents a novel analysis of the throughput performance of the IEEE 802.11 carrier sense multiple access with collision avoidance (CSMA/CA) protocol with a large propagation delay. The throughput analysis is performed by using a real model. A Markov chain model is used to analyze the throughput performance of the IEEE 802.11 CSMA/CA binary exponential backoff algorithm. The results of analysis and computer simulations show that the theoretical throughput is in good agreement with the throughput obtained from computer simulations under the propagation delay less than 20 µs. When the propagation delay is more than 20 µs, the throughput obtained from the simulation results becomes larger than the theoretical throughput because of short-term unfairness. The throughput degradation for a transmission rate of 6 Mb/s and a propagation delay of 40 µs is 16.8 %; this propagation delay corresponds to a transmission distance of 12 km.

Enhancement of IEEE 802.11 and network coding for single-relay multi-user wireless networks

Network coding is a promising technique for improving system performance in wireless multihop networks. In this paper, the throughput and fairness in single-relay multiuser wireless networks are evaluated. The carrier sense multiple access with collision avoidance (CSMA/CA) protocol and network coding are used in the medium access control (MAC) sublayer in such networks. The fairness of wireless medium access among stations (STAs), the access point (AP), and the relay station (RS) results in asymmetric bidirectional flows via the RS; as a result the wireless throughput decreases substantially. To overcome this problem, an autonomous optimization of minimum contention window size is developed for CSMA/CA and network coding to assign appropriate transmission opportunities to both the AP and RS. By optimizing the minimum contention window size according to the number of STAs, the wireless throughput in single-relay multi-user networks can be improved and the fairness between bidirectional flows via the RS can be achieved. Numerical analysis and computer simulations enable us to evaluate the performances of CSMA/CA and network coding in single-relay multi-user wireless networks.

Achievable Region in Slotted ALOHA Throughput for One-Relay Two-Hop Wireless Network Coding

This paper presents achievable regions in slotted ALOHA throughput both without and with network coding for one-relay two-hop wireless networks between two end node groups. In this paper, there are no restrictions on the total traffic and the number of end nodes per group. It follows that the relay node will be generally involved with asymmetric bidirectional traffic. This paper derives closed-form expressions of the throughput and packet delay per group both without and with network coding from a theoretical perspective regardless of whether the buffer on the relay node is saturated or not. Furthermore, we show that the maximum throughput per group with network coding can be achieved at the boundary of the relay buffer saturation and unsaturation which is expressed as the solution of a polynomial equation in two group node traffics. As a result, we clarify the enhancement of the achievable region in slotted ALOHA throughput by applying network coding.

Analysis of Network Coding in Slotted ALOHA with Two-Hop Bidirectional Traffic

This paper deals with two representative bidirectional traffic cases in two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement of multiple unicast and multisource multicast networks. The relay nodes are generally involved with unbalanced multidirectional traffic, but the impact of the unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial for maximizing the achievable throughput of slotted ALOHA systems with network coding in two-hop bidirectional traffic cases.

Novel length aware packet aggregation and coding scheme for multi-hop wireless LANs

This paper proposes a length aware packet aggregation and coding (LAPAC) scheme that uses packet aggregation and network coding (NC) to improve the throughput of single-relay multi-user wireless networks. Besides, this paper clarifies that the throughput is improved by optimizing the minimum contention window sizes in the IEEE 802.11 based single-relay multi-user wireless networks with LAPAC subject to the constraint achieving fairness between uplink and downlink flows. Computer simulation results show that the throughput of the LAPAC scheme is about 10% higher than that of the conventional ones. The optimized minimum contention window sizes are derived by computer simulations and theoretical analysis. The optimized minimum contention window sizes obtained from theoretical analysis are in good agreement with those obtained from computer simulations, when the number of wireless stations is less than or equal to 15. Furthermore this paper shows that LAPAC scheme outperforms the conventional ones in the case of not only single-rate networks but also multi-rate networks.

Coded packet immediate access for contention-based wireless relay networks

This paper proposes a medium access control (MAC) protocol with network coding on relay nodes for contention-based multihop wireless relay networks. The proposed protocol is called coded packet priority access (CPPA) protocol in which coded packets have higher transmission opportunity than non-coded native packets at relay nodes. In this paper, the performance of coded packet immediate access (CPIA) protocols, which are a subclass of CPPA protocols, is evaluated for single-relay bidirectional symmetric traffic and upper and lower bounds of analytical throughput are derived for any given node traffic. It is shown that the lower bound approximates to the throughput obtained from computer simulations with high accuracy. The conventional slotted ALOHA protocol with network coding (S-ALOHA/NC) is required to adapt the transmission probability of relay node to a rational function of node traffic so as to maximize the throughput whereas the CPIA protocol achieves the maximal throughput only if the relay node transmits no native packets. Furthermore it is clarified that the CPIA protocol is superior to the S-ALOHA/NC protocol in delay for given retransmission probabilities of user nodes.