This paper presents a digital baseband IC design based on OFDM PHY for a 60GHz proximity communication system. We propose a low computational complexity OFDM demodulator with a carrier frequency offset estimation method in polar coordinates suitable for high-speed parallel architecture. The proposed architecture is implemented in 65nm CMOS technology, and is experimentally verified to achieve the PHY data rate above 2.2Gbps. The digital baseband IC includes a complete functionality of OFDM transceiver with error correcting codecs and MAC.

This paper is concerned with evaluating ad-hoc networks for group-oriented tactical operations. For such operations, a cellular-based ad-hoc network architecture has been constructed for real-time multimedia communications. To assess the suitability of this network, its performance has been compared with conventional peer-to-peer ad-hoc network architectures under various test scenarios using IEEE 802.11 WLAN technology. We have shown that the cellular network, which operates in two modes: infrastructure for intracell and ad-hoc for intercell communications, is more suitable for group-based tactical missions

This paper is concerned with transporting video information via multihop mobile ad-hoc channels. The major problem with transmitting real-time video information over these channels is the issue of link reliability. To improve the quality of the video reception we propose a cross layer feedback control mechanism that can allow the application layer to adapt itself to a dynamically changing network topology. We also present packet transmission strategies capable of recovering video signals under long bursts of packet drops, typical of a route change condition. This feedback control scheme has been developed for transmission of RTP/UDP/IP packets using the emerging H.264/AVC video-coding standard.

This paper presents a packet-loss feedback tracking scheme for the transmission of video signals over mobile channels. The proposed feedback scheme is based on the real time transport control protocol (RTCP), which is designed to provide an end-to-end feedback assessment of transmitted packets on a frame-by-frame basis (video frame). In addition, the frame synchronized RTCP-based feedback scheme is designed to take care of losses of RTCP packets due to bad channels. The video encoder, upon receiving its feedback report, can identify the exact location of the missing packets in the transmitted video frame. The feedback scheme is then applied to transport H.264/RTP/UDP/IP packets in real-time. A packet-loss compensation strategy has been used to assess the quality of the received signal under multipath fading channel conditions.

This paper presents a master/slave cellular-based mobile ad hoc network architecture for multihop multimedia communications. The proposed network is based on a new paradigm for solving the problem of cluster-based ad hoc routing when utilizing existing wireless local area network (WLAN) technologies. The network architecture is a mixture of two different types of networks: infrastructure (master-and-slave) and ad hoc. In this architecture, the participating slave nodes (SNs) in each cluster communicate with each other via their respective master nodes (MNs) in an infrastructure network. In contrast to traditional cellular networks where the base stations are fixed (e.g., interconnected via a wired backbone), in this network the MNs (e.g., base stations) are mobile; thus, interconnection is accomplished dynamically and in an ad hoc manner. For network implementation, the IEEE 802.11 WLAN has been deployed. Since there is no stationary node in this network, all the nodes in a cluster may have to move together as a group. However, in order to allow a mobile node to move to another cluster, which requires changing its point of attachment, a handoff process utilizing Mobile IP version 6 (IPv6) has been considered. For ad hoc routing between the master nodes (i.e., MNs), the Ad hoc On-demand Distance Vector (AODV) Routing protocol has been deployed. In assessing the network performance, field test trials have been carried out to measure the proposed network performance. These measurements include packet loss, delays under various test conditions such as a change of ad hoc route, handoffs, etc.

In many applications, such as construction, manufacturing, ground robotic vehicles, and rescue operations, there are many issues that necessitate the capability of transmitting digital video and that such transmissions should be performed wirelessly and in an ad-hoc manner. Recently, we proposed an ad-hoc, cluster-based, multi-hop network architecture for video communications (see Gharavi, H. and Ban, K., 3G Wireless Conference, 2002). For implementation, the IEEE 802.11 FHSS wireless LAN system using 2GFSK modulation was employed. To enhance the overall throughput rate for higher quality video communications, we present a performance evaluation of the IEEE 802.11 FHSS when 4GFSK modulation option is selected. Unfortunately, the 2 Mb/s system utilizing 4GFSK modulation is not very efficient in terms of RF range. Therefore, to improve its performance for multi-hop applications, a combination of diversity and non-coherent Viterbi based receiver is considered. For the video transmission part, we have considered a bitstream. splitting technique together with a packet-based error protection strategy to combat packet drops under multipath fading conditions. Finally, the paper presents simulation results, including the effects of receiver design and diversity on the quality of the received video signals.

In this paper, we propose a new packet recognition and signal acquisition scheme with an adaptive linear filter based on a least mean square (LMS) algorithm for code-division multiple access (CDMA) packet systems. In CDMA systems, conventional receivers with matched filtering suffer from the near-far problem due to multiple access interference (MAI). In general, closed-loop power control is used in order to reduce the influence of the near-far problem. However, closed-loop power control is unsuitable for packet systems. Hence, in order to eliminate the influence of the near-far problem, we focus on an adaptive receiver based on an LMS algorithm for packet recognition and signal acquisition in CDMA packet systems.

Abstract Recently, we proposed an ad hoc, cluster‐based, multihop network architecture for video communications using IEEE 802.11 FHSS (Frequency Hopping Spread Spectrum) wireless LAN (WLAN) technology with 2GFSK (2‐level Gaussian Frequency Shift Keying) modulation capable of 1 Mb s−1 transmission. To increase the transmission rate to 2 Mb s−1 for higher‐quality video communications, we evaluated the performance of the IEEE 802.11 FHSS system when a 4GFSK modulation option is selected. Since the 2 Mb s−1 system utilizing 4GFSK modulation is not very efficient in terms of Radio Frequency (RF) range, to improve its performance for multihop applications a combination of diversity and noncoherent Viterbi equalizer are considered. For video transmission, we employed a bitstream‐splitting technique together with a packet‐based error‐protection strategy to combat packet drops under multipath fading conditions. The real‐time transport protocol (RTP), user datagram protocol (UDP), and Internet protocol (IP) are used for video streaming. This includes an RTP packetization scheme to control the packet size and to improve the error‐resilient decoding of the partitioned video signal. The paper includes the simulation results showing the effects of the receiver design and diversity on the quality of the received video signals. Copyright © 2002 John Wiley & Sons, Ltd.

In multipath fading channels, the direct-sequence spread spectrum (DS/SS) technique is often employed because of the capability to resolve signals from different paths and realize path diversity at the receiver. This advantage of DS/SS, however, is only when the time difference of propagation delay between paths is greater than a chip duration. In indoor communications, the delay spread is often very small and the above condition on the delay and chip duration is no longer satisfied, and this performance improvement by the path diversity with conventional DS/SS systems cannot be expected. In this paper we propose a new diversity technique for indoor wireless communication systems where delay spread is smaller than a chip duration. In this system, the transmitter sends signals at the same time from multiple antennas with intentional time delays, which allow a receiver to distinguish and combine the signals from different antennas.