Complexity Evaluation of the Low Data Rate Prototype Solution in the "My Personal Adaptive Global Net (Magnet Beyond)" Project

One of the goals of Magnet Beyond [1] is to design and implement short-range air interfaces that exhibit good performance in term of robustness, flexibility, and power requirements for Personal Area Network (PAN) applications. Two air interfaces are addressed the FM-UWB [2][3][4] for the low data rate (LDR) and the MC-SS for the HDR[12]. These air interfaces constitute the communication media in the user vicinity and are therefore a key component for the wireless PAN. This contribution describes the complexity aspects related to the physical implementation of the LDR transceivers that will be used for the Magnet Beyond air interfaces. The document addresses the integrated platforms respectively from a complexity point of view covering both PHY and MAC aspects. The emphasis is on a structured methodology to minimize the power consumption of the transceiver.

Introduction
Personal area network are expected to play an increasing
important role in future wireless systems. A proliferation
of low data rate sensor devices is envisioned. These
devices must be able to communicate across various
networks in order to provide seamless end-to-end service.
At the physical and link level, several factors are critical
in order to realize a nomadic PAN: co-existence with
other systems, robustness to interference and the
availability of low cost, low power devices. In this paper,
we examine the activities undertaken within the IST
project Magnet Beyond to prove the concept of nomadic
PAN employing low cost, low data rate ultra wideband
communication links between personal devices and a
handset, or mobile bridge.
One of the objectives of MAGNET Beyond [1] is to
design, develop, demonstrate and validate the concept of
a flexible wireless PAN that supports resource-efficient,
robust, ubiquitous Pilot Services in a secure,
heterogeneous networking environment for mobile users.


The radio platform supporting the Pilot Services in
MAGNET Beyond is a multimode terminal covering from
1 kbps up to 130 Mbps data rates using two air interfaces:
? FM-UWB for the LDR (< 250 kbps)
? MC-SS for the HDR (< 130 Mbps)
An example of this multimode scenario is shown in Figure
1 where a central notebook uses both LDR and HDR
radio links to connect to various devices applications.
In this contribution the focus will be on the LDR
platform.
First the Magnet Beyond LDR transceiver design
objectives are introduced. Next the physical layer design
methodology is presented and illustrated for the receiver
gain partitioning. Finally we give some insights on what a
PHY-aware MAC design has to achieve.


II. MAGNET BEYOND LDR TRANSCEIVER DESIGN OBJECTIVES
Table I provides some specifications of the Magnet
Beyond LDR radio transceiver.
The main LDR radio objectives are:
? Reliable communications over 10 m range
(WPAN)
? Low power consumption

Reliable communications can be obtained by having
sufficient receiver sensitivity, which is defined as the RF
signal yielding a reference BER value. The RF SNR
required for obtaining this BER value in turn depends on
the modulation scheme, the implementation loss in the
demodulator as well as the noise generated by the frontend.
The receiver noise figure ultimately determines the
receiver sensitivity.
Since the transmission power PTX (typically PTX -14 dBm
for BRF = 500 MHz) and bandwidth are fixed by
regulations [9], the received power depends on the
distance and propagation conditions. Assuming free space
propagation and isotropic antennas at fc = 4.5 GHz the
received power will be typically in the order of -80 dBm
for a distance of 10 meters.


***********Table I FM-UWB LDR radio characteristics****************
RF centre frequency LB/ HB 4.5 GHz 6.4 ÷ 8.7 GHz
Channel bandwidth >500 MHz
RF output power -14 dBm
Sub-carrier frequency 1- 2 MHz
Sub-carrier modulation FSK, ? = 1,
Raw bit rate ? 250 kbps
Receiver sensitivity -80 dBm
TX, RX switching time ? 10 ?s
Latency (at PHY level) < 1 ms @ 100 kbps
RX synchronisation time < 50 bits
Power consumption RX 7.5 mW
Power consumption TX 3.5 mW
*****************************************************************

Note that no single type of UWB antenna is ideal for all
conditions. Some dipole types are best for stand-alone
use. Slot antennas have significant potential for designs
integrated within the PCB structure. Cylindrically
symmetric bicone and volcano smoke antennas have
excellent omnidirectional radiation properties across a
very broad band, and have been extensively reported.
However they are not considered here as their size and
cost are not compatible with low cost consumer PAN
devices.
Measurements on commercially available small (flat or
near flat) UWB antennas showed that that the directivity
of these antennas is typically 2 dB, and that their
efficiency is around 65 % (-2 dB) resulting in an overall
gain of 0 dBi.
III. RADIO COMPLEXITY
Constraints like power consumption and the available IC
technology impact circuit complexity and cases can be
found where a given radio can't be realized in a given
technology for a given power consumption. The LDR
radio is a low complexity, low-power approach using
digital techniques in the subcarrier processing (baseband)
and relying on analog RF techniques for a low power
circuit implementation of the RF parts of the transceiver
[2][3][4].

The complexity of a PAN device implementation can reside in a number of places:

? RF (analog) circuits
? Baseband analog circuits
? Baseband digital circuits
? Calibration circuits
? Sensor circuitry and interfaces

[...]




REFERENCES

[1] IST-FP6-IP-027396, MAGNET Beyond project, www.ist.magnet.org
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