Copyright © 2009
Dr. Wolf Wireless GmbH
All Rights reserved
|
History
The research work of many years in the area of coding technique
lead to many important results for the development of modern
wireless solutions / systems. Among these research activities CCF
(Cross Correlation Function) procedure was produced. The
CCF-procedure, originally designed for the application in
ATM-Networks is exactly the coding which is applied to the OQPSK
modulation according to the IEEE standard 802.15.4V2003.
On the basis of the CCF procedures the technology PSSS (Parallel
Sequence Spread Spectrum) was developed.
This document
describes
the basic principles of PSSS and its multipath fading resistance.
Key Challenges of Today's RF World
Today's RF technologies provide largely unbalanced answers to a
divergent set of requirements. Key challenges in RF communications
are today:
Range: To maximize the coverage for Tx power
permitted / chosen.
Non line of sight environments:
To transmit
reliably in non line of sight environments with multipath fading.
Interference: To operate under disturbances both
through human made and atmospheric noise.
Coexistence: To minimize disturbance of other RF
systems.
Efficiency: To offer efficient use of the RF
spectrum. To be efficient in power consumption. To be efficient in
physical implementation.
Today's RF technologies
MPSK, QAM, OFDM etc. Features: High
single-station throughput, high specific and absolute data rates,
efficient use of RF spectrum. Disadvantages: Low
range, susceptible to interference, complex & fragile in
implementation, sensitive to multipath fading (except OFDM).
High power consumption (especially OFDM).
DSSS, O-QPSK Features:
Processing gain provides better range and robustness against
interference. Disadvantages:
Low specific data
rates, not efficient in use of spectrum, limited throughput in
existing bands.
FHSS. Features: Robust against
multipath fading, good coexistence with other networks based on
same or other RF technology. Disadvantages:
High effort for management of hopping, inherits issues of
underlying modulation, not suitable for high-throughput systems,
decreasing data rate caused by multipath fading.
Combinations of technologies in today's RF
communication standards mitigate the problems and extend
applications, but do not solve the underlying issues.
Most of the consumer wireless applications are based on wireless
technologies, such as Bluetooth, OFDM (WLAN) etc., operating in
specially allocated, license free, frequencies (ISM bands) which
have limited capacity (bandwidth). As more wireless applications
utilize the same bands their efficient use of the frequency
spectrum is essential to provide the increasing number of users
with higher data transmission speeds, more robustness, better
range-coverage at a lower price tag of the wireless IC and
sub-system. OEM, IC manufacturers and standardization groups
(IEEE, ZigBee, WiFi etc.) have been searching for new wireless
technologies and solutions which can overcome these challenges
and limitations.
Demand indicates that high data rate applications (like WLAN,
audio and video) will mainly operate in the higher 2.4 and 5.8
GHz bands, resulting in higher interference in these bands.
Therefore OEMs and the IEEE standards committees have realized
the advantage of the Sub-1GHz band (868/915MHz) for low power
applications such as sensor, monitoring & control or active
RFID. China and other Asian countries have announced their
intention to open new license free Sub-1GHz bands in 2006.
Traditional radio technologies and RF IC designs, current
wireless chips cannot offer high data rates, more than
20/40Kbit/s, in the Sub-1GHz band. Due to high frequency physics
2.4GHz band technologies are not able to provide better coverage
with the result that OEMs are asking for wireless solutions
which can provide both the advantage of greater coverage and
higher data transmission speeds at lower complexity (cost).
With the introduction of PSSS (Parallel Sequence Spread
Spectrum) technology the transmission efficiency can be
increased by a factor of up to 10, with highest multi path
robustness and extended coverage/range of existing wireless
solutions by a multiple factor. The enhancement of the PSSS
technology is the base for the unique link budgets at 250 kbps
of our PSSS based IEEE802.15.4-2006 platform. The enhanced
performance is even the reason for very low PER in multipath
fading environments. Fore more details look on products
and the presentation
here.
|