In this paper, we propose a Distributed Request based CDMA Reservation ALOHA protocol to support multi-class services, such as voice, data, and videophone services, efficiently in multi-rate transmission cellular systems. The proposed protocol introduces a frame structure composed of an access slot and an transmission slot and an adaptive access permission probability based on the estimated number of contending users for each service, in order to control MAI by limiting the access to slots. It can provide voice service without the voice packet dropping probability through the proposed code assignment scheme, unlike other CDMA/PRMA protocols. The code reservation is allowed for voice and videophone services. The low-rate data service basically uses the remaining codes among the codes reserved for the voice service, but it can also use the codes already assigned to voice calls during the their silent periods to utilize codes efficiently. On the other hand, the high-rate data service uses the codes reserved for itself and the remaining codes among the codes reserved for the videophone service. Using the analytic method based on the Markov-chain subsystem model for each service including the handoff calls in uplink cellular systems, we show that the proposed protocol can guarantee the constant GoS for the handoff calls even with a large number of contending users through the proposed code assignment scheme and the access permission probability. Also, we show that the data services are integrated efficiently on the multi-rate transmission environment.

To prevent performance degradation of TCP due to packet losses in the smooth handoff by the route optimization extension of Mobile IP standard, a few packet buffering methods have been proposed. The packet buffering at the BS recovers the packets dropped during an inter-subnetwork handoff, by forwarding the buffered packets at the previous BS to the new BS to which the mobile host is connected after handoff. However, when the mobile host user moves to a congested BS in a new foreign subnetwork, those buffered packets are likely to be dropped at the new BS. Thus, as well as the TCP connections of the mobile host which have moved into the new BS, the already existing TCP connections of the new BS experience severe performance degradation. This effect is due to the increased congestion by the forwarded burst packets; all of the TCP connections can initiate their congestion control algorithms simultaneously, i.e., global synchronization. This paper will consider a general case where a mobile host user moves into a congested BS of a new foreign subnetwork. We analyze the influence of the packet buffering on the TCP performance in the new BS, for the Drop-Tail and Random Early Detection (RED) buffers. Simulation results show that although the RED buffer gives better handoff performance than the Drop-Tail buffer, it cannot avoid a large decrease in the TCP throughputs due to global synchronization, when a TCP connection is added at the BS by an inter-subnetwork handoff. Finally, we discuss some methods that can address the negative effect of the packet buffering method.

This paper considers an efficient scheduling policy for Bluetooth Medium Access Control (MAC) and its parameter optimization method. The proposed algorithm improves performance as well as supports Quality of Service (QoS) simultaneously. Since Bluetooth is basically operated with a Round Robin (RR) scheduling policy, many slots may be wasted by POLL or NULL packets when there is no data waiting for transmission in the queues of the polled pair. To overcome this link wastage problem, several algorithms have been proposed. However, they have some limitations such as a heavy signaling overhead or no consideration of QoS. Therefore, we have proposed an efficient Bluetooth MAC scheduling algorithm, Differentiated K-Fairness Policy (Diff-KFP), which guarantees improved throughput and delay performance, and it can also lead to differentiated services. That is, if the parameter of the proposed algorithm is optimized, we can satisfy the QoS requirement of each master-slave pair and thereby keep communications in progress from interruption, which is a source of throughput degradation. Simulation results show that our algorithm has remarkably improved the performance and gratifies the QoS requirements of various applications.