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Iterative decoding with intentional snr/sir reduction invention
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5 views | #20070248190 | Prev - Next | USPTO Class 375 | About this Page Iterative decoding with intentional snr/sir reduction
USPTO Application #: 20070248190Title: Iterative decoding with intentional snr/sir reductionAbstract: The excess signal-to-interference ratio (SIR) or the like of a communication channel is determined by repeatedly decoding received information with successively reduced effective SIR. The step size in an outer power control algorithm, for example a Jump Algorithm, such as that commonly used for transmit power control in communication systems can then be adaptively adjusted based on the excess SIR, enabling faster convergence. Decoder hardware already present in a user equipment, such as a mobile telephone or other receiver, can advantageously be used. (end of abstract)
Agent: Potomac Patent Group PLLC - Fredericksburg, VA, USInventor: Johan NilssonUSPTO Applicaton #: 20070248190 - Class: 375340000 (USPTO)Related Patent Categories: Pulse Or Digital Communications, Receivers, Particular Pulse Demodulator Or DetectorThe Patent Description & Claims data below is from USPTO Patent Application 20070248190.
Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND
[0001] This invention relates to electronic digital communication systems
and more particularly to receivers in wireless communication systems.
[0002] Digital communication systems include time-division multiple access
(TDMA) systems, such as cellular radio telephone systems that comply with
the GSM telecommunication standard and its enhancements like GSM/EDGE,
and code-division multiple access (CDMA) systems, such as cellular radio
telephone systems that comply with the IS-95, cdma2000, and wideband CDMA
(WCDMA) telecommunication standards. Digital communication systems also
include "blended" TDMA and CDMA systems, such as cellular radio telephone
systems that comply with the universal mobile telecommunications system
(UMTS) standard, which specifies a third generation (3G) mobile system
being developed by the European Telecommunications Standards Institute
(ETSI) within the International Telecommunication Union's (ITU's)
IMT-2000 framework. The Third Generation Partnership Project (3GPP)
promulgates the UMTS and WCDMA standards. This application focusses on
WCDMA systems for simplicity, but it will be understood that the
principles described in this application can be implemented in other
digital communication systems, including fourth generation (4G) systems
that are under discussion and development.
[0003] WCDMA is based on direct-sequence spread-spectrum techniques, with
pseudo-noise scrambling codes and orthogonal channelization codes
separating base stations and physical channels (terminals or users),
respectively, in the downlink (base-to-terminal) direction. Since all
users share the same radio frequency (RF) resource in CDMA systems, it is
important that each physical channel does not use more power than
necessary if system capacity is not to be wasted. This is achieved by a
transmit power control (TPC) mechanism, in which, among other things,
base stations send TPC commands to users in the downlink (DL) direction
and the users implement the commands in the uplink (UL) direction and
vice versa. The TPC commands cause the users to increase or decrease
their transmitted power levels by increments, thereby maintaining target
signal-to-interference ratios (SIRs) for the dedicated physical channels
(DPCHs) between the base stations and the users. The DPCHs include
dedicated physical data channels (DPDCHs) and dedicated physical control
channels (DPCCHs) in the UL and the DL. A DPDCH carries higher-layer
network signaling and possibly also speech and/or video services, and a
DPCCH carries physical-layer control signaling (e.g., pilot
symbols/signals, TPC commands, etc.). WCDMA terminology is used here, but
it will be appreciated that other systems have corresponding terminology.
Scrambling and channelization codes and transmit power control are well
known in the art.
[0004] FIG. 1 depicts a communication system such as a WCDMA system that
includes a base station (BS) 100 handling connections with, in this
example, four mobile stations (MSs) 1, 2, 3, 4. In the downlink, BS 100
transmits to each mobile station at a respective power level, and the
signals transmitted by BS 100 are spread using orthogonal code words. In
the uplink, MS 1-MS 4 transmit to BS 100 at respective power levels. Each
BS, which is called a Node B in 3GPP parlance, in the system serves a
geographical area that can be divided into one or more cell(s). The BSs
are coupled to corresponding radio network controllers (RNCs, not shown
in FIG. 1) by dedicated telephone lines, optical fiber links, microwave
links, etc. An RNC directs MS, or user equipment (UE), calls via the
appropriate BSs, and the RNCs are connected to external networks such as
the public switched telephone network (PSTN), the Internet, etc. through
one or more core network nodes, such as a mobile switching center (not
shown) and/or a packet radio service node (not shown).
[0005] WCDMA is designed to operate at low signal-to-noise ratios (SNRs)
or SIRs, and therefore the WCDMA algorithms, for instance, SIR estimation
algorithms and automatic frequency control (AFC) algorithms, are designed
for such scenarios. It will be understood that SNR and SIR are
substantially interchangeable in a communication system such as a CDMA
system in which interferers (e.g., other users) are noise-like. For
example, the SIR estimation algorithm, which is used in the TPC scheme to
achieve sufficient quality of service (QoS), is designed to be used at
low SIRs. QoS is often quantified by block error rate (BLER). It will be
understood that, in WCDMA systems (and other communication systems that
employ direct-sequence (DS) spread-spectrum techniques), the noise (N)
includes thermal noise and interference because the spreading of the
signals makes interference signals appear noise-like (i.e., spread out in
frequency and with a level in the noise floor) due to the interference
signals' "wrong" spreading codes.
[0006] Power control in most modern CDMA communication systems is handled
by a combination of an outer loop TPC and an inner loop TPC. The SIR is
used for the inner loop because it is assumed to have an almost
one-to-one mapping to the BLER. The outer loop, which operates with a
slower response rate than the inner loop, compensates for residual
mismatch between the SIR and the BLER. TPC and SIR-to-BLER mapping are
well known in the art, and are described in, for example, U.S. Patent
Application Publication No. US 2005/0143112 by Jonsson, U.S. Pat. No.
6,771,978 to Kayama et al., and Louay M. A. Jalloul et al., "SIR
Estimation and Closed-Loop Power Control for 3G", Proc. 58th Vehicular
Technology Conf., pp. 831-835, IEEE, Orlando, Fla. (October 2003).
[0007] In a communication system such as that depicted by FIG. 1, the BS
transmits predetermined pilot symbols on the UE's DPCH. The BS also
transmits pilot symbols on a common pilot channel (CPICH), and a UE
typically uses the CPICH pilot symbols in estimating the impulse response
of the radio channel to the BS. It will be recognized that the UE uses
the CPICH pilots for channel estimation, rather than the DPCH pilots, due
to the CPICH's typically higher SNR. The UE uses the DPCH pilots mainly
for SIR estimation, i.e., for DL TPC.
[0008] For example, Section 5.2.3.1 of 3GPP TS 25.214, "Physical Layer
Procedures (FDD) (Release 6)", ver. 6.3.0 (September 2004) specifies that
the UE shall generate TPC commands to control the network transmit power
and send them in a TPC field of the UL DPCCH. Annex B.2 of TS 25.214
describes the UE's generating TPC commands for the DPCCH/DPDCH based on
an estimate of the actual SIR and on a SIR reference, or target. The SIR
estimate SIR.sub.est is used with the SIR target SIR.sub.ref by the UE to
generate TPC commands according to the following rule: [0009] if
SIR.sub.est>SIR.sub.ref, generate a TPC command requesting a power
decrease, and if SIR.sub.estразделы
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