Integration Interval Determination and Decision Threshold
Optimization for Improved TRPC-UWB Communication
Systems
Abstract: Integration interval and decision threshold
issues were investigated for improved transmitted
reference pulse cluster (iTRPC-) ultra-wideband
(UWB) systems. Our analysis shows that the bit error
rate (BER) performance of iTRPC-UWB systems can
be significantly improved via integration interval
determination (IID) and decision threshold
optimization. For this purpose, two modifications can
be made at the autocorrelation receiver as follows.
Firstly, the IID processing is performed for
autocorrelation operation to capture multi-path energy
as much as possible. Secondly, adaptive decision
threshold (ADT) instead of zero decision threshold
(ZDT), is used as estimated optimal decision threshold
for symbol detection. Performance of iTRPC-UWB
systems using IID and ADT was evaluated in realistic
IEEE 802.15.4a UWB channel models and the
simulation results demonstrated our theoretical
analysis.
Key words: ultra-wideband (UWB); improved
transmitted reference pulse cluster (iTRPC);
integration interval determination (IID); adaptive
decision threshold (ADT)
I. INTRODUCTION
Noncoherent ultra-wideband (UWB) communication
systems have received considerable attention from
both academic and industry due to their
low-complexity and low-power consumption [1-8].
Among them, transmitted reference (TR) signaling in
conjunction with autocorrelation receiver (AcR) has
become one of the two popular noncoherent
ultra-wideband (UWB) systems (the other popular
scheme is the noncoherent UWB system with energy
detector) [1]. TR-UWB systems do not need channel
estimation and accurate synchronization [9-10].
However, in order to avoid inter-pulse interference
(IPI), a large delay line between reference pulses and
data pulses is required in TR signaling [11]. Such an
impractical stringent requirement for the long
wideband delay line is a major challenge for the
implementation of TR-UWB systems [12-13].
Therefore, transmitted reference pulse cluster (TRPC)
was proposed as an improved TR signaling to avoid
the long delay line [14]. TRPC signaling has a more
compact and uniform spacing between reference
pulses and data pulses that repeat every
seconds.
Although this structure will introduce the IPI, results
reported in [14] show that two benefits in terms of
signal energy efficiency and noise reduction can be
achieved using TRPC structure and they significantly
exceed the penalty caused by the IPI. Therefore,
TRPC-UWB systems have been further investigated
in various interesting issues in recent years [15-23].
Based on the TRPC signaling, an improved
TRPC scheme, referred to as iTRPC, was recently
proposed in [20] to obtain better bit error rate (BER)
performance. In iTRPC signaling, a number of “zero”
pulses are inserted at the end of each reference pulse
clusters (RPC) and each data pulse clusters (DPC).
According to this improvement, the IPI can be
effectively reduced and more multi-path components
can be exploited for data detection. However, the
zero-padding space still does not exceed the maximum
multi-path delay. Therefore, the IPI still exists in
iTRPC.
In this paper, iTRPC with integration interval
determination and decision threshold optimization
(iTRPC-IAD) is investigated as the modified iTRPC.
Firstly, considering the dispersive energy distribution
of multi-path components, the integration interval is
determined at the autocorrelation receiver using the
methods proposed in [21], in which more energy can
be captured than iTRPC. Moreover, since iTRPC
cannot completely remove the IPI, zero decision
threshold (ZDT) is not the optimal decision threshold
and hence the decision threshold is optimized by
employing adaptive decision threshold (ADT) [22].
Based on the two modifications mentioned above,
iTRPC-IAD can achieve better BER performance
compared with iTRPC.
The reminder of this paper is organized as
follows. Section II describes the signal and channel
models. Integration interval determination and
decision threshold optimization are presented for
iTRPC in section III and IV, respectively. Section V
gives the simulation results to demonstrate the
superiority of iTRPC-IAD. Finally, section VI
provides the conclusions.
II. SIGNAL AND CHANNEL MODELS
In this section, we introduce the signal and the
channel models for iTRPC-UWB systems.
2.1 Original TRPC Signaling
Before discussing the iTRPC, it is necessary to
introduce the original TRPC signaling. In TRPC
signaling, the information packet is first modulated as
a BPSK symbol sequence
, which is then