In this paper, we propose a modified scheme of MSODB and PMS, called Predictive User Mobility Behavior (PUMB) to improve performance of resource reservation and call admission control for cellular networks. This algorithm is proposed in which bandwidth is allocated more efficiently to neighboring cells by key mobility parameters in order to provide QoS guarantees for transferring traffic. The probability is used to form a cluster of cells and the shadow cluster, where a mobile unit is likely to visit. When a mobile unit may change the direction and migrate to the cell that does not belong to its shadow cluster, we can support it by making efficient use of predicted nonconforming call. Concomitantly, to ensure continuity of on-going calls with better utilization of resources, bandwidth is borrowed from predicted nonconforming calls and existing adaptive calls without affecting the minimum QoS guarantees. The performance of the PUMB is demonstrated by simulation results in terms of new call blocking probability, handoff call dropping probability, bandwidth utilization, call successful probability, and overhead message transmission when arrival rate and speed of mobile units are varied. Our results show that PUMB provides the better performances comparing with those of MSODB and PMS under different traffic conditions.

In wireless OFDM systems, the system performance is suffered from frequency offset and symbol timing offset due to the Doppler effect. Using the discrete Fourier transform (DFT) and inverse discrete Fourier transform (IDFT) for traditional signal transformation from the time-domain into frequency-domain, and vice versa, the system performance may be severely degraded. To make the OFDM system that can tolerate the above problems, we have considered that the harmonic transform can be applicable to the traditional signal transformation, thereby improving the system performance. In this paper, we combine the good characteristics of harmonic transform and instantaneous frequency to be a novel transformation for wireless OFDM systems. We propose a modified discrete harmonic transform (MDHT) which can be performed adaptively. Our proposed scheme called the modified discrete harmonic transform OFDM (MDHT-OFDM scheme). We derive the equations of the novel discrete harmonic transform which are suitable for wireless OFDM systems and the novel channel estimation cooperated with the novel transformation. The proposed channel estimation is performed in both time-domain and frequency-domain. The performance of a MDHT-OFDM scheme is evaluated by means of a simulation. We compare the performance of a MDHT-OFDM scheme with one of the conventional DFT-OFDM scheme in the term of symbol error rate (SER). MDHT-OFDM scheme can achieve better performance than that of the conventional DFT-OFDM scheme in mitigating the Doppler spread.

This paper presents an analysis of the Slotted DS-CDMA system with modified node components in order to construct a load control structure in which the service rates of each node can be dynamically adapted without using feedback information. In contrast to the traditional Slotted DS-CDMA which is widely represented with single queue, prior emphasis of the approach is laid on the usage of an additional queue which is applied to manage the collided packet traffic while its queue size is also used as a load control parameter. Semi-Markov process is applied to describe the statistic behavior of the system in steady state. Trade-offs between two major performance parameters, i.e., delay and throughput, are presented and compared with those of the traditional system. Results obtained from the simulation and numerical analysis using queuing concept are compared. With these results, an advantage performance for group packets is shown, and we finally extend the concept based on the obtained results to describe a simple algorithm using one way control message as the tool to alleviate the stability problem.

Store-and-forward communication networks with no effective means of flow control are subject to congestion under heavy load conditions. In this paper a distributed congestion control policy, called PF-C, with nodal buffer management strategy based on traffic priorities is proposed and analyzed. The priority of a packet is depended upon the number of hops it has traveled and the number ob hops it has to travel to reach its destination. More importantly, packets are identified into classes according to their priorities. The limited number of buffers (limit value) at any node to be occupied by each class of packets are assigned. The mechanism of this policy is that, a packet which arrived at a given node is rejected if the total number of allocated buffers exceeds a limit value corresponding to its class. Rejected packets are dropped from the network and considered as lost. This policy is analyzed in the context of symmetrical networks, whereby a queuing model is developed. Finally, network throughput which is an example of system performance, is formulated in terms of offered load, total number of buffers in a node and the limit values. Numerical applications to loop networks clearly demonstrate the good behavior of this policy to achieve the maximum network throughput.

One of the important techniques in communication system design is the composition of service and protocol specifications. In this paper, we have presented a new approach to the composition technique based on the weak bisimulation concept. The main objective is to combine service specifications and protocol specifications individually and simultaneously. The composition technique can maintain the equivalence between the composed service and protocol specifications. LOTOS language terms are utilized to describe the communication specifications. The application on the asynchronous model is presented. Moreover, a support system of the composition technique is developed and presented in this paper.