Joint algorithm and architecture development for 4G mobile communications JADE

PhD: Søren Skovgaard Christensen

 Casestory

1. General

PhD Programme

• Wireless Communications

Working Title

• Adaptive Air Interface for Low Complexity Wireless Terminals

Partners

• Søren Skovgaard Christensen (CISS)
• Joint Advanced Development Enabling 4G (JADE) industrial research project at Center for TeleInFrastruktur (CTIF) at Aalborg University.

Time Frame

• March 2004 – February 2007

2. Summary

This project deals with design aspects of the upcoming 4G system related to basic transmission techniques. The main focus of this project is design of algorithms that will lead to a flexible air interface, while decreasing the terminal complexity. This is relevant since the essential criteria for 4G to become successful are that it will be cheaper and deliver higher Quality of Service (QoS) than current 3G solutions. The project takes a starting point in a well known pre-processing concept for low complexity terminals, where basically some intense signal processing tasks traditionally processed at the terminal are moved to the access point (base station) where the complexity issues are less stringent. We strive to compare this concept with basic OFDM and try to incorporate new advanced techniques from recent research such as multi-user MIMO and multi-antenna based inter-cell interference mitigation. Essentially it is expected that the studies will lead to new information about the feasibility of the pre-processing concept as a potential 4G air interface.

Figure 1. Layered Architecture

3. What is 4G?
The 4G system is projected to be a convergence platform extended to all network layers for a wide variety of new high-quality services. These network layers span from Fixed Wired (no mobility), through Personal Networks, Hot Spots, Metropolitan, Cellular, and to the Distribution Networks. The support and availability of these networks will enable the end user to be connected "almost" anywhere and sharing the networks will smooth the problem related to spectrum limitation of 3G cellular networks. Thus 4G has recently been referred to as a “Network of Networks”.

According to this definition, the 4G vision may soon be reality. 3G networks are currently being deployed and IP hotspots based on the WLAN technology is gaining popularity in densely populated areas. Lacking is however important issues such as seamless usage and service quality guarantees. Therefore, as a countermove to the combination of structured 3G and ad-hoc WLAN network deployment, large technology vendors are trying to push new IP access technologies such as WiMAX into the market in order to improve e.g. coverage and QoS.

In this work we take a similar approach. Specifically we investigate different design aspects of a brand new IP access technology, which is intended to compete with existing technologies. Roughly speaking the new access technology is targeting both hotspot and cellular conditions (with high mobility) and is intended to enable simple deployment to gradually make the existing access technologies redundant. The infrastructure is intended to be based on distributed wireless routers directly connected to the IP-backbone, see Figure 2.

Figure 2. Conceptual Diagram of IP Infrastructure

Easy and cheap deployment is achieved by circumventing an additional mobile core network as appears in 3G and instead connecting radio access routers directly to the IPcore network as done when deploying WLAN hotspots. This, however, introduces some technical challenges regarding self-configuration of the radio resources (time, frequency, space) among the different access points, which in 3G is centrally controlled.

4. Project Focus
The project deals with design aspects mainly at the physical layer (air interface) and the data link control layer, corresponding to layer 1 and 2 of the OSI model – see Figure 1. The design involves a new transmission technique and a new error correction technique (physical layer) and may be described as a cross-layer optimization problem of the physical and data link control layers.

The primary target is lower terminal complexity – defined as the signal processing complexity at the physical layer. This will be obtained by shifting some of the functionality at the terminal to the access point, which will experience higher complexity. This tradeoff is reasonable as argued in Figure 3.

Figure 3. Design Trade-off Justification

Besides lower terminal complexity it is expected that the layer 1 and 2 cross-layer design will have another desirable property, namely lower overall time delay as observed from layer 3. Time delay is a very important Quality of Service parameter.