Jeffrey R. Foerster

The effects of multipath interference on the performance of UWB systems in an indoor wireless channel

Multipath propagation for the indoor wireless channel is very complicated and difficult to predict. Several papers have been written attempting to apply an analytical model for this channel to help systems engineers evaluate various architectural components of a wireless system, including modulation, multiple access, and waveform design techniques, without having to resort to empirical data collection. This paper attempts to apply one of these analytical models, known as the /spl Delta/-K model, to help study the performance of an ultra wide band (UWB) system and look at performance trade-offs for different multilevel modulations as well as the benefits of RAKE reception.

Toward enhanced mobile video services over WiMAX and LTE [WiMAX/LTE Update]

Wireless networks are on the verge of a third phase of growth. The first phase was dominated by voice traffic, and the second phase, which we are currently in, is dominated by data traffic. In the third phase we predict that the traffic will be dominated by video and will require new ways to optimize the network to prevent saturation. This increase in video traffic is one of the key drivers of the evolution to new mobile broadband standards like WiMAX IEEE 802.16m and 3G LTE and LTE-Advanced, motivating the need to enhance the video service capabilities of future cellular and mobile broadband systems. Therefore, it is important to understand both the potential and limitations of these networks for delivering video content in the future, which will include not only traditional video broadcasts, but also video streaming and uploading in the uplink direction. In that vein this article provides an overview of technology options for enabling multicast and unicast video services over WiMAX and LTE networks, quantifies and compares the video capacities of these networks in realistic environments, and discusses new techniques that could be exploited in the future to further enhance the video capacity and quality of user experience.

Design challenges for very high data rate UWB systems

Ultrawideband (UWB) is a promising radio technology for networks delivering extremely high data rates at short ranges. In this paper, different approaches to the physical layer system design for such networks are studied, and some of the challenges and opportunities inherent in their design and implementation are compared. For example, the use of extremely short duration pulses offers great possibilities for position location, but makes the timing synchronization task more complex. The ultra-wide bandwidth offers excellent frequency diversity and multipath resolution, but the channel estimation and multipath combining tasks are correspondingly more challenging. A pulse based UWB system (or impulse radio, IR-UWB) and a novel pulsed multicarrier UWB system are compared, emphasizing timing acquisition and performance in multipath. Some other differences, including interference avoidance, equalization, etc. are briefly dealt with.

Detect and Avoid (DAA) Mechanisms for UWB Interference Mitigation

Worldwide ultra-wideband (UWB) radio regulations are slowly taking shape, and are reaching the final stages of work. The main reasons for the continued debate has of course been the potential interference that can be caused by UWB radios to other radios with which they would share the spectrum. Specifically for the case of broadband wireless access (BWA) systems serving indoor subscriber stations (SS), it has been proposed to impose a requirement that UWB systems should detect and avoid interference to the downlinks of such BWA SS. In this paper we discuss some of the aspects of such solutions, and present some results and description of the ongoing work in this area

Multiband Media Access Control in Impulse-Based UWB Ad Hoc Networks

We propose a MAC protocol for use in multihop wireless networks that deploy an underlying UWB (ultra wide band)-based physical layer. We consider a multiband approach to better utilize the available spectrum, where each transmitter sends longer pulses in one of many narrower frequency bands. The motivation comes from the observation that, in the absence of a sophisticated equalizer, the size of a slot for transmitting a UWB pulse is typically dictated by the delay spread of the channel. Therefore, using a wider frequency band to shorten the transmission time for each pulse does not increase the data rate in proportion to the available bandwidth. Our approach allows data transmissions to be contiguous and practically interference free, and, thus, highly efficient. For practicality, we ensure the conformance of our approach to FCC-imposed emission limits. We evaluate our approach via extensive simulations, and our results demonstrate the significant advantages of our approach over single-band solutions: the throughput increases significantly and the number of collisions decreases considerably. Finally, we analyze the behavior of our MAC protocol in a single-hop setting in terms of its efficiency in utilizing the multiple bands

A multiband mac protocol for impulse-based UWB ad hoc networks

Ultra Wide Band (UWB) technology offers a promis- ing high capacity solution for wireless networks with short-range links. However, MAC and higher-layer ad hoc network protocols that exploit the UWB technology are yet to mature. In this paper, we propose a MAC protocol for use in multi-hop wireless networks that deploy an underlying UWB based physical layer. We adopt a multi-band approach wherein we divide the available UWB band- width into multiple simultaneously usable bands. The motivation comes from the following observation: in the absence of a sophis- ticated equalizer, the size of a slot for transmitting a UWB pulse is typically dictated by the delay spread of the channel. There- fore, using a wider frequency band to shorten the transmission time for each pulse may not increase the data rate in proportion to the available bandwidth. Thus, we consider a multi-band ap- proach to better utilize the available spectrum, where each trans- mitter sends longer pulses in one of many narrower frequency bands. Unlike previous single hopped schemes that rely on time- hopping, our approach allows data transmissions to be contigu- ous, and thus, highly efficient. The approach also ensures that data communications are practically interference free and are only subject to thermal noise effects. To ensure that our proposed ap- proach is tightly knit with the underlying physical layer, we discuss physical-layer dependencies and the conformance of our approach to FCC-imposed emission limits. We evaluate our approach via ex- tensive simulations. Our simulation results demonstrate the signif- icant advantages of our approach over single-band solutions: the throughput increases significantly, and the number of collisions decreases considerably.

A multibanded system architecture for ultra-wideband communications

The FCC ruling in 2002 allowing for the unlicensed deployment of ultra-wideband (UWB) devices for communications purposes in the 3.1-10.6 GHz band has sparked great interest in the industry. In particular, the IEEE 802.15.3a task group is currently developing a standard for high-rate, short-range wireless communication systems that is expected to use UWB technology. One of the main challenges for UWB system design is minimizing the possible interference to other narrowband systems, while, at the same time, dealing with the large interference that may be coming from these narrowband systems into the UWB receiver. Traditional UWB systems have used very short time impulses that occupy several giga-hertz of bandwidth. This approach makes it difficult to efficiently avoid other system that may be sharing the same band. This paper will describe a channel model that has been adopted by the industry to evaluate the merits of different UWB physical layer approaches and introduce an alternate approach to a high-rate UWB system that is based upon the concatenation of multiple narrower band UWB waveforms.

Efficient cross-layer resource allocation for H.264/SVC video transmission over downlink of an LTE system

We formulate a PHY/APP cross-layer resource allocation problem for efficient transmission of video streams in a multiple-user LTE downlink system. To achieve a predetermined video PSNR, the number of bits needed for different users is calculated using a parameterized Rate-Distortion (RD) model proposed by [4]. We design an admission policy which assigns frequency-time OFDMA channel resource to video users based on a cross layer metric. For the admitted users, we use a tracking algorithm to serve the users as the video source content and channel conditions evolve. The goal of the resource allocation is to maximize the number of admitted users from a fixed user population and guarantee that the video quality of admitted users will achieve the predetermined PSNR threshold. The performance of the proposed algorithms is compared to four baseline algorithms which exploit different levels of cross layer knowledge about the channel and source characteristics, and the results show benefits from cross-layer optimization.

Distortion-aware MIMO link adaptation for enhanced multimedia communications

In wireless multimedia communications, optimizing the quality of user experience is a major design goal, which is often quantified by the end-to-end distortion between the actual multimedia source at the encoder and its reconstructed version at the decoder. Joint source-channel coding (JSCC) techniques aim to optimize codec and radio system parameters in order to minimize end-to-end distortion and yield enhanced quality of user experience when compared with separate source-channel coding techniques. With the motivation of applying JSCC-based cross-layer optimizations to PHY/MAC layer design for practical wireless systems, this paper proposes new techniques for MIMO link adaptation toward enhanced multimedia communications. In particular, we propose new distortion-aware MIMO link adaptation techniques toward the selection of modulation and coding schemes (MCS) and MIMO space-time modulation (including MIMO diversity and spatial multiplexing) schemes with the objective of minimizing end-to-end distortion, different from classical approaches that aimed for other optimizations such as maximizing spectral efficiency or goodput. Furthermore, we investigate the performance of distortion-aware MIMO link adaptation in realistic link-level simulation (LLS) and system-level simulation (SLS) environments based on orthogonal frequency division multiplexing (OFDM) under broadband frequency-selective fading with special focus on multicast broadcast services (MBS), and demonstrate their advantages over goodput-maximizing MIMO link adaptation techniques in terms of reduced end-to-end distortion and higher peak signal-to-noise ratio (PSNR).

A new binary conflict resolution-based MAC protocol for impulse-based UWB ad hoc networks

Ultra wide band (UWB) technology offers a promising high capacity solution for short-range wireless ad hoc networks, as in home networks or in wearable ad hoc networks. In this paper, we propose a novel multi-band MAC protocol for use in small ad hoc networks that deploy an underlying UWB based physical layer. In our approach, we divide the available UWB bandwidth into multiple simultaneously usable bands. In the absence of a sophisticated equalizer, the size of a slot for transmitting a UWB pulse is typically dictated by the delay spread of the channel. Therefore, using a wider frequency band to shorten the transmission time for each pulse does not increase the data rate in proportion to the available bandwidth. A multi-band approach that uses a plurality of bands that adhere to FCC specifications, with slightly elongated pulse durations, provides a solution that can effectively utilize the UWB spectrum. Our approach is based on the idea of conflict resolution using binary ‘something’/‘nothing’ feedback, which has not been widely studied in wireless and specifically in UWB networks. Our protocol unites binary conflict resolution and multi-band utilization to effectively utilize the available bandwidth. To ensure that our proposed approach is tightly knit with the underlying physical layer, we discuss physical–layer dependencies and the conformance to FCC-imposed emission limits. We evaluate our approach via extensive simulations. Our simulation results demonstrate the significant advantages of our approach over single-band solutions: the throughput increases significantly, and the number of collisions decreases considerably. Copyright