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13.12.2017 : 4:32

Workpackage 4 -Physical Layer Architecture

The WP4 leader is Rohit Datta of TUD.

The WP4 study on QoSMOS transceiver architectures requires a number of inputs from other workpackages. Important inputs are expected particularly from WP2 and WP3. WP2 clarifies QoSMOS system aspects and the QoSMOS architecture and will provide important guidelines for the receiver sensitivity, interference limits, spectral masks, link budgets and signalling/pilot channels. WP3 will provide various spectrum sensing schemes and latency requirements, which have to be analyzed in terms of computational complexity. Hence, the digital processing of the sensing receiver is to be dimensioned in a way to not exceed the latency requirements for the sensing part of the QoSMOS system.

 

Objectives

This workpackage investigates transceiver architectures, allowing opportunistic exploitation of frequency white spaces (WS) for wireless data communications. The design of such devices is particularly difficult mainly for two reasons. On the one hand, signal generation should ensure ultra-low out of band radiation to strictly avoid harmful interference to incumbent signals. On the other hand, the receivers should exhibit high sensitivity in order to explore white spaces, i.e., to sense even very weak incumbent signals. 

Apart from these fundamental requirements, there are even more engineering challenges which have to be addressed throughout this workpackage. Typically, white spaces as in the TV bands are not consecutively placed in the spectrum, but they exhibit strong fragmentation. In order to efficiently exploit all detected white spaces, a system is required which can cope with strong spectrum fragmentation and which is able to perform aggregation of several WS by one single wide-band signal. Hence, the QoSMOS transceiver should be wide band and be able to fulfil the following demands: 

• Low out of band radiation to avoid harmful interference to incumbent signals

• Easy equalization despite wideband nature of the transmit signal 

• Frequency agile white space allocation, flexible signal bandwidth

• Digital implementation to reduce the requirements of the analogue front-end

• Flexible design to adapt to various transmission conditions

Recent studies provided by the FP6 project ORACLE indicate the efficient usage of multi carrier systems to flexibly exploit vacant spectrum by switching subcarriers on and off. However, the most prominent multi carrier system OFDM is known to cause strong spectral leakage even when using pulse shaping techniques or guard carriers. Hence as further objective of WP4, some novel concept is to be researched which combines the flexibility and simplicity of OFDM with stronger interference reduction mechanisms. In this respect it should be clarified, whether existing transceiver concepts for signal generation (DAC – digital to analogue conversion) are sufficient to meet the stringent spectral masks in the legacy bands. Some study items from the engineering side which are to be considered in WP4 are therefore:

• Complexity of the digital baseband processing - What are the design tradeoffs?

• Settling time when moving to another frequency

• Power efficiency – Where are the bottlenecks of such a QoSMOS transceiver?

 

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