This chapter considers the Multiband Orthogonal Frequency Division Multiplexing (MB-
OFDM) modulation and demodulation with the intention to optimize the Ultra-Wideband
(UWB) system performance. OFDM is a type of multicarrier modulation and becomes the
most important aspect for the MB-OFDM system performance. It is also a low cost digital
signal component efficiently using Fast Fourier Transform (FFT) algorithm to implement the
multicarrier orthogonality. Within the MB-OFDM approach, the OFDM modulation is
employed in each 528 MHz wide band to transmit the data across the different bands while
also using the frequency hopping technique across different bands. Each parallel bit stream
can be mapped onto one of the OFDM subcarriers.
Quadrature Phase Shift Keying (QPSK) and Dual Carrier Modulation (DCM) are currently
used as the modulation schemes for MB-OFDM in the ECMA-368 defined UWB radio
platform. A dual QPSK soft-demapper is suitable for ECMA-368 that exploits the inherent
Time-Domain Spreading (TDS) and guard symbol subcarrier diversity to improve the receiver
performance, yet merges decoding operations together to minimize hardware and power
requirements. There are several methods to demap the DCM, which are soft bit demapping,
Maximum Likelihood (ML) soft bit demapping, and Log Likelihood Ratio (LLR) demapping.
The Channel State Information (CSI) aided scheme coupled with the band hopping
information is used as a further technique to improve the DCM demapping performance.
ECMA-368 offers up to 480 Mb/s instantaneous bit rate to the Medium Access Control
(MAC) layer, but depending on radio channel conditions dropped packets unfortunately
result in a lower throughput. An alternative high data rate modulation scheme termed Dual
Circular 32-QAM that fits within the configuration of the current standard increasing system
throughput thus maintaining the high rate throughput even with a moderate level of
dropped packets.
[1]
Boris Lembrikov.
Novel Applications of the UWB Technologies
,
2011
.
[2]
Fabrice Seguin,et al.
Analogue 16-QAM demodulator
,
2004
.
[3]
G.R. Aiello,et al.
Design of a multiband OFDM system for realistic UWB channel environments
,
2004,
IEEE Transactions on Microwave Theory and Techniques.
[4]
J. Foerster,et al.
Channel modeling sub-committee report final
,
2002
.
[5]
Wenzhen Li,et al.
An efficient low-cost LS equalization in COFDM based UWB systems by utilizing channel-stateinformation (CSI)
,
2005,
VTC-2005-Fall. 2005 IEEE 62nd Vehicular Technology Conference, 2005..
[6]
Anuj Batra,et al.
Multi-band OFDM Physical Layer Proposal
,
2003
.
[7]
Tommy Oberg.
Modulation, detection, and coding
,
2001
.