Contents 1 Wireless Networks 1 1.1 Introduction ...................................... 1 1.1.1 History of Wireless Networks ........................ 2 1.1.2 Wireless Data Vision ............................. 5 1.1.3 Technical Challenges ............................. 7 1.2 The Wireless Channel ................................. 8 1.2.1 Path loss ................................... 9 1.2.2 Shadow Fading ................................ 10 1.2.3 Multipath Flat-fading and Intersymbol Interference ............. 11 1.2.4 Doppler Frequency Shift ........................... 12 1.2.5 Interference .................................. 13 1.2.6 Infrared versus Radio ............................ 13 1.2.7 Capacity Limits of Wireless Channels .................... 14 1.3 Link Level Design .................................. 15 1.3.1 Modulation Techniques ............................ 15 1.3.2 Channel Coding and Link Layer Retransmission .............. 16 1.3.3 Flat-Fading Countermeasures ..

As the cellular and PCS world collides with Wireless LANs and Internet-based packet data, new networking approaches will support the integration of voice and data on the composite infrastructure of cellular base stations and Ethernet-based wireless access points. This paper highlights some of the past accomplishments and promising research avenues for an important topic in the creation of future wireless networks. In this paper, we address the issue of cross-layer networking, where the physical and MAC layer knowledge of the wireless medium is shared with higher layers, in order to provide efficient methods of allocating network resources and applications over the Internet. In essence, future networks will need to provide ”impedance matching ” of the instantaneous radio channel conditions and capacity needs with the traffic and congestion conditions found over the packet-based world of the Internet. Further, such matching will need to be coordinated with a wide range of particular applications and user expectations, making the topic of cross-layer networking an increasingly important one for the evolving wireless build-out. 1

This paper focuses on congestion control over multihop, wireless networks. In a wireless network, an important constraint that arises is that due to the MAC (Media Access Control) layer. Many wireless MACs use a time-division strategy for channel access, where, at any point in space, the physical channel can be accessed by a single user at each instant of time. In this paper, we develop a fair hop-by-hop congestion control algorithm with the MAC constraint being imposed in the form of a channel access time constraint, using an optimization based framework. In the absence of delay, we show that this algorithm are globally stable using a Lyapunov function based approach. Next, in the presence of delay, we show that the hop-by-hop control algorithm has the property of spatial spreading. In other words, focused loads at a particular spatial location in the network get "smoothed" over space. We derive bounds on the "peak load" at a node, both with hop-by-hop control, as well as with end-to-end control, show that significant gains are to be had with the hop-by-hop scheme, and validate the analytical results with simulation.

Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However, most of the proposed solutions require distributed space–time coding algorithms, the careful design of which is left for future investigation if there is more than one cooperative relay. We propose a novel scheme that alleviates these problems and provides diversity gains on the order of the number of relays in the network. Our scheme first selects the best relay from a set of available relays and then uses this “best ” relay for cooperation between the source and the destination. We develop and analyze a distributed method to select the best relay that requires no topology information and is based on local measurements of the instantaneous channel conditions. This method also requires no explicit communication among the relays. The success (or failure) to select the best available path depends on the statistics of the wireless channel, and a methodology to evaluate performance for any kind of wireless channel statistics, is provided. Information theoretic analysis of outage probability shows that our scheme achieves the same diversity-multiplexing tradeoff as achieved by more complex protocols, where coordination and distributed space–time coding for relay nodes is required, such as those proposed by Laneman and Wornell (2003). The simplicity of the technique allows for immediate implementation in existing radio hardware and its adoption could provide for improved flexibility, reliability, and efficiency in future 4G wireless systems.

Imagine that, while on a business trip to Paris, you decide to take a few extra days to sample the city's museums. When you buy your museum pass, you are given a virtual tour guide device --- a small PDA that can deliver information about specific pieces in the museum system as well as general information about the city. This device communicates via wireless networks. In or near a museum, the device has access to a high-speed micro-cellular network; in the rest of the city, it makes use of the GSM infrastructure. The user can ask this device to elaborate on specific sites or pieces, display related information, or perform geographically-based queries. These requests are satisfied by applications such as a customized Web browser and a video playback application. When within range of a museum's high-quality network, the displayed information is of excellent quality: images are at high resolution and color, and video is delivered in full motion. However, when the user strays away fr...

Bandwidth and power constraints are the main concerns in current wireless networks because multihop, ad hoc mobile wireless networks rely on each node in the network to act as a router and packet forwarder. This dependency places bandwidth, power, and computation demands on mobile hosts which must be taken into account when choosing the best routing protocol. In recent years, protocols that build routes based "on demand" have been proposed. The major goal of on-demand routing protocols is to minimize control traffic overhead. In this paper, we perform a simulation and performance study on some routing protocols for ad hoc networks. Distributed Bellman-Ford, a traditional table-driven routing algorithm, is simulated to evaluate its performance in multihop wireless networks. In addition, two on-demand routing protocols (Dynamic Source Routing and Associativity-Based Routing) with distinctive route selection algorithms are simulated in a common environment to quantitatively measure and co...

This article presents an overview of soft handoff, an idea which is becoming quite important because of its use in the IS-95 code-division multiple access (CDMA) cellular phone standard. The benefits and disadvantages of using soft handoff over hard handoff are discussed, with most results drawn from the available literature. The two most well-known benefits are fade margin improvement and higher uplink capacity, while disadvantages include increased downlink interference and more complex implementation. Handoff parameter optimization is extremely important, so various studies on the trade-offs to be considered when selecting these parameters are surveyed, from both the link quality and resource allocation perspectives. Finally, research directions and future trends are discussed.

Many MAC sub-layer protocols for supporting the usage of directional antennae in ad hoc networks, have been proposed in literature. However, there remain two open issues that are yet to be resolved completely. First, in order to fully exploit the spatial diversity gains due to the use of directional antennae, it is essential to shift to the exclusive usage of directional antennae for the transmission and reception of all the upper layers frames. This would facilitate maximal spatial re-use and will efface the phenomena of asymmetry in gain. Second in the presence of mobility the MAC protocol should incorporate mechanisms by which a node can efficiently locate and track its neighbors. In this paper we propose a new polling based MAC protocol that addresses both the issues in an integrated way. We perform analysis and extensive simulations to understand the performance of our scheme in terms of its ability to maintain connectivity, the achieved utilization efficiency, and throughput. We find that each node, on average, can achieve a per node utilization of about 80 % in static and about 45 % in mobile scenarios. Our protocol is seen to outperform both the traditional IEEE 802.11 MAC protocol and previosuly proposed protocols for use with directional antennae that provide partial solutions to solve the aforementioned problems. Finally, we also study the sensitivity of our protocol to various system parameters. 1

Undersea observatories connected to shore with fiber-optic cable will provide scientists with long-term measurements from deep-ocean sensors. Proposed regional observatories include NEPTUNE which will traverse a three thousand kilometer path on the Juan de Fuca plate in the North Pacific. The NEPTUNE backbone includes nodes spaced approximately 100 km apart where additional branches may be added, and a variety of sensors supporting different scientific disciplines will located at each node and along the branches. The fiber optic and power cable creates a backbone that easily supports many smaller regions (cells) covered by wireless communication. An acoustic system extends the reach of the observatory in the area around each cell, allowing additional instruments to be added without installing dedicated cables. The utility of the wireless extension is highly dependent upon the range of the link, its energy efficiency and the total capacity of a cell. The objective of this paper is to explore these issues and discuss design, implementation, and performance of the wireless network. I.

In this paper we have modelled the behavior of the CDMA cell using clustered Poisson process. We have found that when the RF dynamics of the cell is modelled using this two dimensional description of the user arrival process, the size and the capacity of the cell are completely determined by the spatial traffic density and stability arguments. This is much like provisioning a server in a queueing system. This paper is an extension of the work presented in [1] by incorporating the idea of a clustered nature of customers in a cell.