It has been shown that cooperative transmissions improve the throughput of slotted ALOHA. However, the impact of the capture effect on cooperative slotted ALOHA, which has practical significance for radio channels with fading, shadowing and the near-far effect, remains unknown. This paper proposes and analyzes a random access protocol which incorporates cooperative transmissions and the capture effect in slotted ALOHA. Numerical results illustrate that this scheme improves the throughput by 56% in Rayleigh fading channels when the capture ratio is 3 dB as compared to cooperative slotted ALOHA without the capture effect.

To enable secondary transmissions in cognitive radio (CR) networks, the medium access control (MAC) protocol design for CR networks is an important but challenging issue. In this paper, we propose a cognitive packet reservation multiple access (Cog-PRMA) protocol for the CR/secondary users (SUs) sharing a common channel with time division multiple access (TDMA) primary users (PUs). This Cog-PRMA protocol not only achieves the goal of supporting secondary packet transmissions without interfering the PUs' transmissions, but also takes advantage of PRMA to improve the CR network bandwidth efficiency. In this paper, the Cog-PRMA protocol and frame structure are fully described, and theoretical network throughput for the CR networks is derived using the speech model and two dimensional Markov chain in this paper. Simulation results show that effective secondary communication is achieved and there are noticeable increases in the total network throughput (primary plus secondary).

Slotted Aloha is an effective random access protocol and can also be an important element of more advanced media access protocols. This paper investigates slotted Aloha in a radio environment with multiple access points. Specifically, we examine the impact of multi-access-point (multi-AP) diversity on the performance of slotted Aloha. The paper considers both omni-directional (OM) and beamforming (BF) antennas at transmission nodes. This leads to the investigation and comparison of four different network scenarios, i.e., OM with multi-AP diversity, OM without multi-AP diversity, BF with multi-AP diversity and BF without multi-AP diversity. Performance evaluations and comparisons are presented in terms of throughput and average packet delay.

Cooperative diversity is an effective technique for transmission performance improvement over fading channels. In this paper, through the use of a virtual antenna array, a time division multiple access (TDMA) based cooperative media access control (MAC) protocol, Cooperative TDMA (C-TDMA), is proposed to enable cooperative transmissions in Rayleigh fading channels to improve the probability of correct packet reception and system throughput. A C-TDMA throughput expression is derived using a Markov chain model. Numerical results show that the throughput of conventional TDMA can be improved by over 40% through the use of the cooperative MAC designs.

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.

Both TDMA and CSMA are effective media access protocols, which can also be important elements of more advanced protocols. In this paper, we investigate TDMA and slotted 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 TDMA is used for primary users to access the channel and secondary users use slotted CSMA to sense the time slots of TDMA and transmit their packets during idle time slots. A Rayleigh fading channel is considered and we derive the throughput of TDMA and slotted CSMA for the primary and secondary networks.

Time division multiple access (TDMA) is suitable for the energy efficiency requirement of wireless sensor networks (WSN) since it avoids idle listening and collisions. We introduce a two-tier-TDMA structure to describe and analyze a TDMA-based converge cast WSN. In our model, each cluster head is responsible for forwarding data from ordinary nodes of its cluster to a super cluster head. This paper presents derivations and simulations of the two-tier TDMA performance in terms of throughput. We consider scenarios with different cluster sizes, signal fading and inter-cluster interference.

Slotted Aloha is an effective random access protocol and can also be an important element of more advanced media access protocols. This paper investigates slotted Aloha in a radio environment with multiple access points. Specifically, we examine the impact of multi-access-point (multi-AP) diversity on the performance of slotted Aloha. The paper considers both omnidirectional (OM) and beamforming (BF) antennas at transmission nodes. This leads to the investigation and comparison of four different network scenarios, i.e., OM with multi-AP diversity, OM without multi-AP diversity, BF with multi-AP diversity and BF without multi-AP diversity. Performance evaluations and comparisons are presented in terms of throughput.

Slotted Aloha is an effective random access protocol and can also be an important element of more advanced media access protocols. This paper investigates slotted Aloha in a cognitive radio environment where one access point provides services for both primary users and secondary users. Considering packet capture effects in a Rayleigh fading channel, we present the mathematic derivations of system throughput and average delay for primary users and secondary users. In order to minimize the interference from secondary users to primary users, higher transmission power levels are assumed for primary users.

Convergecast is a communication structure for wireless sensor networks (WSN) in which data flow from multiple nodes into one node. We use a two-tier slotted Aloha model to analyze the throughput and average packet delay of a convergecast mode based on slotted Aloha. In our model each node has a buffer and we use Equilibrium Point Analysis (EPA) approach to study the model. Rayleigh fading is assumed in the analysis.

Although cluster-based routing schemes are active research topics in mobile ad hoc networks (MANET), few people investigated the throughput of MANET under such schemes. This paper attempts to obtain throughput of a special cluster-based MANET in which the distance between each ordinary node and a cluster head is one hop. When the underlying media access control (MAC) protocol is slotted Aloha, we propose a model called two-tier aloha to describe such a communication scenario. In this model each cluster head is responsible for collecting data from the ordinary nodes in its cluster and forwarding data to a super cluster head. Channel contentions following slotted Aloha exist in communications from ordinary nodes to cluster heads and from cluster heads to the super cluster head. We use a Markov chain to analyze this model and present an approach to obtain a theoretical network throughput. The theoretical results are validated through simulations.