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Issue Date: March 2008

Addressing wireless challenges

March 2008
Frost & Sullivan Technical Insights

Supporting state-of-the-art multimedia services could be made possible with the emergence of efficient multi-hop relay networks.

The past few years have seen broadband wireless technology establish itself as one of the most rapidly growing areas in the field of telecommunications. The current trends and demands are to deliver rich multimedia services such as voice, video, high definition TV (HDTV) with guaranteed quality of service (QOS). To support such state-of-the-art multimedia services, a high-speed data transmission is necessary. This could be made possible with the emergence of efficient multihop relay networks.
Why multihop networks?
Currently the world is witnessing a rising trend in advanced networking capabilities. As the network infrastructure becomes complex it is ideal that the speed of communication increases consequently. The third generation (3G) mobile communication systems have data transmission capability of up to 2 Mbps while high-speed downlink packet access (HSDPA) aims at achieving a maximum rate of around 10 Mbps.
However, information across the Internet is increasing so rapidly that wireless transmission capability will become insufficient sooner rather than later. There is already an increasing demand for peak rates of around 1 Gbps in mobile communication systems. Fulfilling these demands is the task of the promising fourth generation (4G) mobile communications systems, which are expected to emerge around 2011.
As these high-data rates emerge there will however be an important challenge to overcome. As the transmission rate becomes higher, the peak transmit power of a mobile terminal must be increased. Shrinking the size of the cell is one way to avoid larger peak transmit powers. However, if the cell size becomes smaller, the control signal traffic for handover and location registration may increase.
Current deployments suffer from:
* Limited spectrum.

* Very low signal to interference plus noise ratio (SINR).

* Traffic load is non-uniformly distributed, which will cause congestion and traffic oriented issues.
Frost & Sullivan believes that multihop networks could help avoiding scenarios where the problems mentioned above occur. The use of multihop relaying in cellular networks is considered a key practice for increasing data transmission rates and maximising coverage in 4G wireless systems.
Multihop networks - a snapshot
Multihop communication occurs when data travels from the source to the destination node via more than two hops. This feature enables increasing the range of the network by a significant margin.
The number of hops must be carefully evaluated. As the number of hops is directly proportional to the transmission time there must be a constant check on the hop count. Multihop-based networks may also improve system performance thanks to cooperative relay technique, which is accomplished by sending information simultaneously via different paths and combining the received information at the side of the receiver.
A mobile multihop network is a set of mobile nodes which communicate over radio and do not need an infrastructure. These networks are suitable for several types of applications, as they allow the establishment of temporary communication without any pre-installed infrastructure. Due to the limited transmission range of wireless interfaces, in most cases communication has to be relayed over intermediate nodes.
Thus, in mobile multihop ad hoc networks each node also has to be a router. However, the routing is a major challenge in mobile multihop ad hoc networks, which is aggravated by the node mobility. This challenge is overcome by the advent of a new technology and a standard referred as 802.16j or mobile multihop relay (MMR).
MMR - an overview
Mobile multihop relay is an extension of the standard cellular architecture where the area to be covered is divided into cells. However, instead of deploying base stations (BSs) with wired backhaul in each cell, some of the cells are served by a new type of network element called a relay station (RS).
RSs provide access to subscriber stations for a particular area, but they do not connect to a wired backhaul link. Instead, the RSs connect to the BS via wireless links, which we refer to as relay links.
IEEE 802.16j (mobile multihop relay, MMR) standard is intended to enhance the performance of the existing 802.16-2005 products by introduction of RSs. MMR coordinates all radio resources such as frequency re-use, network entry, mobility, routing, scheduling and load distribution, but functionality can be distributed to RS.
Relay technology may also be used to extend range to isolated areas and better in-door coverage can be offered. Mobile multihop relay is also expected to reduce the complexity of future implementations of IEEE 802.16j.
Due to the flexibility that exists in the placement of RS cell sites, MMR can be used to improve the coverage and capacity of existing worldwide interoperability for microwave access (WiMAX) networks, by augmenting the coverage and capacity of cells in the current network. RSs can also be deployed to provide coverage within buildings or moving vehicles such as trains. Moreover, they can be deployed on a temporary basis as well.
Benefits of the technology
Flexible cell site placement: RSs can be deployed on a temporary basis to provide coverage in coverage holes, provide access to remote clusters, to provide capacity in specific areas. The deployment of MMR in the right place is essential since it helps to speed the deployment, and in turn reduces site acquisition and backhaul costs.
Lowering barrier-to-entry: a strategic significance of multihop relaying schemes is to provide solutions for wireless accessibility in developing countries where wired connectivity is unavailable. Wireless multihop networking is strongly believed to facilitate this mission.
From a commercial perspective, the multihop networking paradigm may be utilised to bring commercial value to wireless service providers. A limited number of gateways may be sufficient for a service provider to efficiently and cost-effectively establish its access network.
Overcoming shortcomings of current technology: an interesting example conveying the use of wireless multihop networking is the $100 laptop project to provide computing and networking accessibility to under-privileged areas. In order to maintain the project's objectives, a low-cost networking alternative is needed.
Improves coverage, capacity, QoS at a reduced cost: relays help in decreasing costs. Deploying a base station is very expensive and it can be substituted by using relays stations. The main aim of providing multihop relay networks is to improve the coverage, capacity and to provide advanced QoS.
Load sharing and the inherent multipath redundancy: load sharing aids in improving service since the system can adapt to variations in load and can also handle infrastructure failures with ease. It also has the capability to reduce infrastructure costs since redundant equipment is not necessary.
There are many competing technologies in the research stage for multihop network, however it is expected to take close to five years for their commercial deployment. Telecom giants such as US-based Samsung, Nortel Networks, and Siemens are excelling in research towards effective deployment of multihop relay networks. Since the demand for high-data rates is constantly on the rise, profound activity in this domain is anticipated.
For more information on Frost & Sullivan's technical & market analysis, please contact Patrick Cairns on patrick.cairns@frost.com.


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