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7 - Routing strategies in multi-hop CDMA networks
- Edited by Harald Haas, Universität Bremen, Stephen McLaughlin, University of Edinburgh
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- Book:
- Next Generation Mobile Access Technologies
- Published online:
- 02 September 2009
- Print publication:
- 10 January 2008, pp 186-213
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Summary
Multi-hop relaying routing protocols have been investigated for CDMA air interfaces in conventional cellular scenarios, as described in Chapter 6 and in (Harold and Nix, 2000a) (Harold and Nix, 2000b). This chapter compares the performance of ODMA with direct transmission for cases where links maybe required directly to other nodes, as well as to a controlling (backbone) node, and presents two new routing algorithms.
For an interference-limited system, it is shown that the topology cannot be supported by a conventional (single-hop) system, but that a relayed system is able to provide service. As an enhancement to path loss routing, a new admission control and routing algorithm based on receiver interference is presented which is shown to further enhance performance.
A second new routing algorithm, which considers the interaction between all receivers in the system by means of a ‘congestion’ measure is presented. This approach allows for routing that is optimised for the entire system, not just a particular route under arbitrary starting conditions. This is possible under both central and local parameter gathering scenarios. Through formulating this measure into the power control equations it is possible to determine system feasibility, although this is a conservative criterion due to approximations in the formulation. This congestion-based routing is shown to outperform non-relaying and any previous routing technique in available capacity for the new network topologies, and has the lowest transmitted power requirement of all investigated methods.
8 - Multi-hop DCA
- Edited by Harald Haas, Universität Bremen, Stephen McLaughlin, University of Edinburgh
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- Book:
- Next Generation Mobile Access Technologies
- Published online:
- 02 September 2009
- Print publication:
- 10 January 2008, pp 214-227
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Summary
DCA techniques
Congestion-based routing, as developed in the previous chapter, is shown to require the lowest transmitted power, and in most cases achieves the highest capacity of all the routing algorithms examined in Chapter 5. All of these routing algorithms have allocated TDD time slots on a first-come-first-served basis and according to the rules outlined in section 6.4.1. This allocation only serves to ensure that the limitations of the TDD hardware are considered. It makes no attempt to optimise time slot allocation.
The allocation of time slots with regard to system performance has been shown to be an effective technique to mitigate interference (Haas, 2000). Integrating slot allocation, or DCA, into the routing algorithm would appear to be the most effective approach due to the interactive nature of interference. This approach will also need to conform to the extra limitations imposed by relaying. In addition to the rules in section 6.4.1, it is obvious that the slot allocation must be in the same order as the relays. A combined DCA will allow minimisation of the desired measure, in this case congestion, simultaneously in routing and slot allocation. This chapter develops a combined routing and resource allocation algorithm for TDD-CDMA relaying. It starts by reviewing one such algorithm applicable to TDMA and FDMA. A novel method of time slot allocation according to relaying requirements is then developed. Two measures of assessing congestion are presented based on matrix norms.
6 - UTRA-TDD Opportunity-Driven Multiple Access (ODMA)
- Edited by Harald Haas, Universität Bremen, Stephen McLaughlin, University of Edinburgh
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- Book:
- Next Generation Mobile Access Technologies
- Published online:
- 02 September 2009
- Print publication:
- 10 January 2008, pp 157-185
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Summary
In this and the following two chapters the focus moves away from networks which are controlled centrally by a base station to a hybrid cellular network which permits cellular operation as well as peer-to-peer operation. Essentially we consider multi-hop wireless networks based on opportunity-driven multiple access (ODMA) which will be shown to reduce the overall transmission power in a system, to be resilient to shadowing and to potentially increase the coverage compared with single-hop transmission. However, for simple receivers and low user density, the actual capacity of UTRA-TDD may be marginally reduced from the maximum non-relaying capacity. This chapter begins the study of ODMA based systems by analysing the implications of relaying in a cellular scenario compared to a conventional nonrelaying system. Initially the interference is analysed by investigating the effect of reduced transmitted power resulting from reduced path loss for a link. The effect of shadowing is considered and it is shown that a relaying system is able to benefit from increased zero mean lognormal shadowing by utilising the diversity of paths available. A correlated shadowing model is developed from a previous model considering both distance and angle of arrival (Klingenbrunn and Mogensen, 1999) to include the shadowing correlation between all transceivers, as they may all be available to receive in a relaying environment. It is shown that while this affects the interference pattern the perturbation is not significant.