This paper proposes an adaptive call-occurrence probability (COP) setting method for a slotted-ALOHA based consensus problem. Individual agents in the focused consensus problem control themselves in a distributed manner based on the partial information of overall control system which can be received only from the neighbor agents. In order to realize a reliable consensus problem based on wireless communications, we have to consider several constraints caused by the natures of wireless communications such as communication error, coverage, capacity, multi-user interference, half-duplex and so on. This work first investigates the impacts of wireless communication constraints, especially communication coverage, half-duplex, and multiple-access interference constraints, on the quality of control. To mitigate the impact of multiple-access constraint, we propose an adaptive COP setting method that changes the COP corresponding to the states of communication and control. The proposed adaptive COP based slotted-ALOHA needs the information about the number of neighbor agents at its own and neighbor agents, but can still work in a distributed manner. Computer simulations show that the proposed system can achieve better convergence performance compared to the case with the fixed COP based system.

Higher transmission rates are one of the main characteristics of the fourth-generation (4G*) of mobile communications. These systems are expected to operate at higher frequency bands, which experience larger propagation loss. This results in larger required transmission power, which causes several problems, particularly for uplink communications, as the typical mobile station (MS) has limited transmission power. Multi-hop systems have been proposed to address this problem. In this paper, we consider the issue of random-access (RA) in a multi-hop system. It is clear that a two-hop mobile communication system requires a two-stage RA process. In this paper, we propose a two-stage RA process that is an extension of the RA process of the CDMA-based 3GPP standard. The proposed method uses a hybrid of code division multiple access (CDMA) and Slotted-ALOHA. To realize the proposed two-hop RA, we dedicate one slot for second-hop transmissions in each interval (predefined); we refer to this as the interval slots allocation (ISsA) technique. Numerical analyses and simulations are conducted to evaluate its basic performance in a multi-hop system. The results demonstrate the superior throughput-delay performance of the proposed two-stage RA multi-hop system with ISsA.

This paper examines fairness of service in the up-link of CDMA cellular slotted-ALOHA packet communication systems with site diversity reception. Site diversity rescues the packets originating mainly from near the edge of the cells, whereas packets originating near the base stations can not obtain the benefits of diversity reception. This situation causes an unfairness in packet reception that depends on location of the mobile station. Two transmission control schemes for reducing this unfairness are proposed. In the first scheme, mobile stations control the target received power for the open-loop power control based on the reception level of the pilot signals of the surrounding base stations. In the second, mobile stations control transmit permission probability. Successful packet reception rate, fairness coefficient and throughput performance are evaluated in fading environments with imperfect power control. Computer simulation shows that both schemes improve service fairness for all mobile stations and throughput performances. A performance comparison between the two schemes concludes that transmission power control outperforms transmit permission probability control as a simple technique for maintaining fairness of services.

A new transmit permission control scheme applicable in multi-cell communication systems is proposed. In this scheme, by prohibiting the transmissions from the users with relatively high propagation loss to their connecting hub stations, level of multiple access interference is decreased, and hence throughput characteristics are improved. Moreover, we continue our discussion to propose two adaptive forms of the transmit permission control scheme, in which the prohibition condition becomes more intelligent by considering the level of the offered traffic loads to hub stations. These methods are utilized in a slotted Aloha random transmission of the spread spectrum packets, and on the uplinks of a low earth orbit satellite communication system as an example of the multi-cell systems. It is shown that the adaptive schemes exhibits significantly improved characteristics at all offered traffic loads in these systems.