To meet the bandwidth requirements of multimedia services, multipath transmission is a promising solution. In this paper, we consider multi-access networks, where WiMAX and WiFi links are set up at the same time. Multipath transmission suffers from the intrinsic problem of out-of-order packet delivery. This has an adverse impact on TCP and even UDP-based delay sensitive applications. However, multimedia streaming services allow some tolerance to transmission delay. Motivated by this observation, we investigate how to split multimedia flows over heterogeneous links. Wireless link capacity varies widely over time due to dynamic radio conditions. The capacity variations should be promptly reflected in traffic splitting in order to accomplish an equal load-balance. A practical prototype system has been implemented. We have performed extensive measurements from a prototype system. Through practical experimental results, we could verify two major research goals. One is that multimedia splitting can improve the overall network performance (e.g., the permitted multimedia sessions or the aggregated bandwidth) while still keeping an acceptable media quality. The other is an adaptation capability to varying link quality. It has been widely investigated under various radio conditions and different monitoring intervals. It is shown that the adaptive technique is effective under dynamic radio environments.

Video transmission over mobile worldwide interoperability for microwave access (WiMAX) can be serverly degraded due to the effect of fading and handoff. In this paper, we propose a channel adaptive error resilience scheme for video transmission over mobile WiMAX. When the channel condition begins to trigger handoff, the current frame is stored in the long-term memory for the forward error correction, and the following frames are encoded by using double motion vectors (MVs) in the sense of multi-hypothesis motion compensation. Even if a whole frame is lost, we can reconstruct the following frames using the stored frame in the long-term memory. However, the error propagation still remains in this forward error resilience method. To refresh the erroneous frames to the decoder, the encoder utilizes the channel adaptive refreshing (CAR). In the CAR, the channel rate is first predicted using channel parameter, a carrier to interference and noise ratio (CINR), and the encoder adaptively determines the number of blocks to be encoded in the intra mode based on the feedback information. Performance evaluations are presented to demonstrate the effectiveness of the proposed method.

The institute of electrical and electronics engineers (IEEE) 802.16e is designed to support a wide range of applications with various quality of service requirements. Since MAP signaling overhead can unacceptably be large for voice traffic, IEEE 802.16e suggests the use of multicast sub-MAPs whose messages are encoded according to the channel condition. In this case, it is desirable for the base station to properly choose a modulation and coding set associated with the channel condition. In this letter, we consider the use of an adaptive modulation coding scheme for the multicast sub-MAPs without explicit information on the channel condition. The proposed scheme can achieve the same MAP coverage as the broadcast MAP while minimizing the signaling overhead. Simulation results show that when it is applied to voice-over-internet protocol (VoIP) services, the proposed scheme can significantly enhance the VoIP capacity.

Some OFDMA-based wireless commuication systems, e.g., Wireless Broadband Internet (WiBro) or Worldwide interoperability for Microwave Access (WiMAX), support frequency reuse of 1 to maximize spectral efficiency. One of the efficient methods to reduce co-channel interference (CCI) caused by frequency reuse is fractional frequency reuse (FFR). In this paper, we propose and validate a novel frequency partitioning method and subcarrier assignment mechanism to improve system and individual capacity of mobile systems using FFR.

The cognitive radio system consists of multiple wireless access systems that cover overlapping areas and cognitive terminals that use one or more of the wireless access systems simultaneously. In this paper, we describe the system architecture of a platform for load balancing and throughput enhancement with cognitive radio system. In our platform, each terminal, which can access multiple radio systems, operates with a single local IP address. Based on our platform, we have developed both simulator and testbed system. Through the simulation of and the testing of a testbed system, we prove that systems load balance was achieved between WiMAX and wireless LAN, and total user throughput was increased with the proposed platform. Moreover, load balance to satisfy both real time service and best effort service. These results demonstrate the platform described in the paper can achieve a convergence with plural wireless systems.

The signalling protocol vulnerability opens DDoS problem in Mobile WiMAX networks. This letter proposes an authentication method that uses the unrevealed upper 64 bits of Cipher-based MAC as a solution. It runs for MSs in idle mode and reduces the calculation complexity by 59% under DDoS attack while incurring 1% overhead under normal condition.

As one of the promising techniques in Broadband Wireless Access (BWA), IEEE 802.16 also namely WiMax provides wide-area, high-speed, and non-line-of-sight wireless transmission to support multimedia services. Four service types are defined in the specification of IEEE 802.16 for QoS support. In order to achieve end-to-end multimedia services, 802.16 QoS must be well integrated with IP QoS. In this paper, we propose a framework of cross-layer QoS support in the IEEE 802.16 network. Two novel mechanisms are proposed in the framework for performance improvement: Fragment Control and Remapping. Fragment Control handles the data frames that belong to the same IP datagram in an atomic manner to reduce useless transmission. Remapping is concerned with the mapping rules from IP QoS to 802.16 QoS and is designed to reduce the impact of traffic burstiness on buffer management. Simulation study has shown that the proposed scheme has higher goodput and throughput, and lower delay than the contrast.

With the advent of new Radio Access Technologies (RATs), it is inevitable that several RATs will co-exist, especially in the license-exempt band. In this letter, we present an in-depth adaptation of the proactive time-rearrangement (PATRA) scheme for IEEE 802.11WLAN. The PATRA is a time division approach for reducing interference from a multi-radio device. Because IEEE 802.11 is based on carrier sensing and contention mechanism, it is the most suitable candidate to adapt the PATRA.

A multiband T-shaped monopole antenna for WLAN/WiMAX applications is presented. The T-shaped monopole is comprised of two horizontal arms of different lengths, which generate two separate resonant modes for 2.5/5.5 GHz WLAN/WiMAX bands, and with a shortened parasitic element, which generates a middle resonant mode for 3.5 GHz WiMAX band, for seamless wireless network access applications. The proposed antenna has been successfully simulated and implemented. Both results of simulation and measurement show good agreement. For the lower band from 2.3 to 2.7 GHz, the gain varies in the range of 2.5-3.3 dB, while the radiation efficiency is from 72% to 85% over the band. As for the middle band from 3.3 to 3.7 GHz, the gain varies from 1.5 to 2.0 dB, and the radiation efficiency is from 62% to 70%. As for the upper band from 5.2 to 5.8 GHz, the antenna gain varies from 5.4 to 5.9 dB, and the radiation efficiency is from 63% to 66%.

We present a simple proactive time rearrangement scheme (PATRA) that reduces the interferences from multi-radio devices equipped in one platform and guarantees user-conceived QoS. Simulation results show that the interference among multiple radios in one platform causes severe performance degradation and cannot guarantee the user requested QoS. However, the PATRA can dramatically improve not only the user-conceived QoS but also the overall network throughput.

In this letter, we propose an efficient resource allocation scheme that improves the system performance by reducing the signaling overhead for voice over Internet protocol (VoIP) services in the IEEE 802.16e OFDMA system. We theoretically analyze the performance of the proposed allocation scheme and carry out a computer simulation to evaluate the FA scheme.

The cognitive radio system consists of multiple wireless access systems that cover overlapping areas and cognitive terminals that use one or more of the wireless accesses simultaneously. In this paper, we describe the architecture of the cognitive radio system and the inter-system handover protocols. In the architecture, each cognitive terminal, which can access multiple radio systems, operates with a single local IP address. The control sequence and packet format are designed to achieve fast handover among the radio systems. Based on the architecture, we have developed a testbed system. On this system, we demonstrate that data can be delivered continuously and radio systems can be switched correctly without any packet loss. In addition, we present the result of the evaluation of the end-to-end latency on the testbed system. These testbed results demonstrate the system architecture described in the paper can achieve a cognitive radio system.

Wireless communications technology continues to change and yield new standards for satisfying the user demands. As a result, multiple standards coexist and wireless communications systems supporting different air interfaces cannot interact with one another. Software-defined radio is regarded as the most promising solution to cope with this problem. In this paper, we discuss the design considerations of SDR systems from a base station point of view and propose new architecture which meets the inherent requirements of SDR platform. We then introduce hardware/software of SDR platform we accomplished on the basis of the new architecture. In addition, the results of basic transmission and receiving performance are presented to prove the feasibility of the proposed platform as a base station.