Simple Medium Access Control Protocol Research Articles

Shared Network Effects in Time- versus Event-Triggered Consensus of a Single-Integrator Multi-Agent System

Event-triggered control has the potential to provide a similar performance level as time-triggered (periodic) control while triggering events less frequently. It therefore appears intuitive that it is also a viable approach for distributed systems to save scarce shared network resources used for inter-agent communication. While this motivation is commonly used also for multi-agent systems, a theoretical analysis of the impact of network effects on the performance of event- and time-triggered control for such distributed systems is currently missing. With this paper, we contrast event- and time-triggered control performance for a single-integrator consensus problem under consideration of a shared communication medium. We therefore incorporate transmission delays and packet loss in our analysis and compare the triggering scheme performance under two simple medium access control protocols. We find that network effects can degrade the performance of event-triggered control beyond the performance level of time-triggered control for the same average triggering rate if the network is used intensively. Moreover, the performance advantage of event-triggered control shrinks with an increasing number of agents and is even lost for sufficiently large networks in the considered setup.

Rate selection based medium access control for full-duplex asymmetric transmission

The realization of full-duplex wireless communication is predictable. And asymmetric transmission is a practical and low-cost application scenario, where full-duplex access point (FD_AP) can communicate with two users simultaneously to receive and send packets. While, in an asymmetric transmission, the transmit power of uplink sender decides the uplink and downlink rates because of the inter-client interference, which accordingly restricts the throughput. Besides, the size of packets in uplink and downlink is generally unequal. Therefore, a WIFI network with a FD_AP and half-duplex users is studied in this paper, and a medium access control (MAC) protocol based on power control and rate selection (PCRS) is proposed. PCRS MAC employs a received signal strength based rate selection strategy to select different rates and power for uplink and downlink transmission. Then, FD_AP can establish efficient and reliable full-duplex asymmetric transmission. Simulation results show that PCRS can improve the throughput and the probability of successful asymmetric communication as compared to the distributed coordination function (DCF) and a simple full-duplex MAC protocol without PCRS. Besides, PCRS MAC also maintains a high level of fairness.

Delay analysis and optimality of the renewal access protocol

For many years, the IEEE 802.11 distributed coordination function (DCF) has been widely used as a dominant medium access control (MAC) protocol in wireless networks and a large number of works have been done for analyzing and improving its performance. In our earlier work, as a substitute of the IEEE 802.11 DCF, a simple MAC protocol, called the renewal access protocol (RAP), is proposed. The RAP adopts all of the legacy 802.11 standard but the backoff stage feature. Each terminal selects its backoff counter value from a fixed sized window according to a priori given selection distribution in the RAP, regardless of the packet transmission result. It is shown that, if a Poisson distribution is used as the selection distribution, then the resulting RAP achieves high short-term fairness as well as optimal throughput. In this work, we analyze the relation between delay performance and the selection distribution of the RAP. With the help of effective bandwidth theory, we derive the conditions for the selection distribution of the RAP that optimizes the queue overflow probability. We also construct the delay optimal selection distribution satisfying the optimal conditions for throughput and delay. However, we show that the use of the delay optimal selection distribution results in an extremely slow convergence to steady state compared with that of the Poisson selection distribution. Moreover, we show that the Poisson selection distribution provides near-optimal delay performance. Therefore, we conclude that the use of a Poisson selection distribution is still recommended even from the delay perspective.

An improvement in a simple MAC protocol for cognitive wireless networks

Medium Access Control (MAC) is an important aspect of implementing a cognitive radio network. Ghasemi and Razavizadeh proposed a simple, elegant and efficient MAC protocol for cognitive wireless networks [1]. However, the Ghasemi’s algorithm does not consider the quality of the wireless channel in the decision process. In this paper, an improvement in Ghasemi’s algorithm is proposed to consider the behavior of the wireless channel in the decision process.

Medium Access in Spread-Spectrum Ad Hoc Networks with Multiuser Detection

Conventional medium access control protocols are designed to avoid simultaneous transmissions, based on a simple collision model in the underlying physical layer. Recently, strong physical layer capabilities, enabled by multiuser detection techniques, have been studied in connection with simple medium access control protocols, for example, slotted ALOHA. We think that neither of these extreme approaches is optimum, particularly in general scenarios where network nodes with different signal processing capabilities coexist. Instead of dealing with interferences in either of the two layers alone, both medium access control and physical layer functionalities should be designed to cooperate and complement each other. We discuss several key aspects for designing such a protocol, especially with an emphasis on iterative multiuser detection, which can provide a good tradeoff between performance and complexity. We propose a new protocol called MUD-MAC which satisfies these key aspects. We analyze its throughput bound and also perform numerical simulations. The simulation results show excellent throughput improvements. It is also demonstrated that the MUD-MAC protocol provides certain fairness among network nodes with different signal processing capabilities.