Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
2000-03-14
2003-12-09
Ghayour, Mohammad (Department: 2731)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S267000
Reexamination Certificate
active
06661853
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to communication systems and more specifically to a communication system including multiple independent receivers.
BACKGROUND OF THE INVENTION
FIG. 1
is a diagram illustrating a portion of a prior art cellular communication network. The cellular communication network includes base stations
101
,
102
, and
103
. Base stations
101
,
102
, and
103
provide areas of coverage
104
,
105
, and
106
, respectively, for voice communications. Base stations
101
,
102
, and
103
are located relative to each other to ensure complete coverage, even providing overlapping coverage in fringe regions of these areas of coverage
104
,
105
, and
106
, such as “soft handoff” region
110
.
However, while significant noise can be tolerated for voice communications, high speed data communications are more sensitive to noise. Therefore, high speed data communications require a higher signal-to-noise ratio than voice communications. Since signals become weaker as the distance between antennas increases, signals to and from base stations
101
,
102
, and
103
become weaker as a mobile unit moves farther from the base station. As the signals become weaker, the signal-to-noise ratio decreases. Since high speed data communications require higher signal-to-noise ratios than voice communications, transmission output power levels are increased in order to maintain the same area of coverage for high speed data communications as compared with analog communications. However, limitations on transmission output power normally prevent high speed data channels from maintaining the same area of coverage. Therefore, areas of coverage
107
,
108
, and
109
for base stations
101
,
102
, and
103
, respectively, for high speed data communications are smaller than areas of coverage
104
,
105
, and
106
for voice communications.
Since the locations of many base stations were chosen for the purposes of voice communications, base stations
101
,
102
, and
103
are sometimes too far apart to provide seamless coverage for high speed data communications. For example, none of areas of coverage
107
,
108
, or
109
for high speed data communications include region
111
. Thus, a mobile unit located in region
111
would be denied service for high speed data communications. Thus, a technique is needed to increase the reliability of high speed data communications and to allow uninterrupted high speed data communications across multiple base stations.
FIG. 6
is a block diagram illustrating a prior art receiver. A base station such as base stations
101
,
102
, and
103
includes such a receiver. The receiver includes antenna
601
, demodulator and filter
602
, automatic gain control (AGC) circuit
603
, first despreader
604
, nth despreader
605
, channel correctors
606
and
607
, deskewer/combiner
608
, deinterleaver
609
, and decoder
610
. Antenna
601
is coupled to demodulator and filter
602
. Demodulator and filter
602
is coupled to AGC circuit
603
. AGC circuit
603
:is coupled to a plurality of despreaders, illustrated by first despreader
604
and nth despreader
605
. The despreaders are coupled to a plurality of channel correctors, illustrated by channel correctors
606
and
607
. The channel correctors are coupled to deskewer/combiner
608
. Deskewer/combiner
608
is coupled to deinterleaver
609
. Deinterleaver
609
is coupled to decoder
610
.
Decoder
610
provides a metric signal and data. Decoder
610
may be a Viterbi decoder. The metric signal provided by the decoder
610
is a correlation output of the most likely path chosen by the decoder from among many possible paths, which may be expressed in the form of a trellis diagram. This correlation output from the decoder of the most likely path chosen indicates the most likely data sequence based on the input to the decoder.
When a mobile unit is transitioning from an area of coverage of one base station to an area of coverage of another base station, the mobile unit operates in a “soft handoff” mode where the mobile unit communicates with more than one base station. For example, the mobile unit may communicate with three different base stations during a “soft handoff.” A “soft handoff” differs from a “hard handoff” in that, for a “hard handoff,” a mobile unit is in communication with only one base station at any given time, and the transition from one base station to another occurs at a specific moment in time. An example of a “soft handoff” process begins with a mobile unit communicating with a first base station within the area of coverage of the first base station. As the mobile unit moves toward a second base station, the mobile unit enters a region of “soft handoff” where the mobile unit is able to communicate with both the first base station and the second base station. If the mobile unit continues away from the first base station, the mobile unit leaves the region of “soft handoff” and remains in communication with the second base station.
The mobile unit transmits a reverse link signal to the base stations with which it communicates. To receive the reverse link signal transmitted by the mobile unit, each of these base stations attempts to decode the reverse link signal and sends its received frame data to a base station controller (BSC). Thus, the BSC receives the received frame data from each base station with which the mobile unit communicates.
FIG. 2
is a block diagram illustrating a prior art technique for determining a received datum from a plurality of data from a plurality of independent receivers. Base stations
201
,
202
, and
203
include receivers
204
,
205
, and
206
, respectively. Each of receivers
204
,
205
, and
206
provides a metric signal and data to a base station controller
207
. The base station controller
207
of the prior art functions as a multiplexer that simply chooses a frame of data from the base station with the largest metric signal. The base stations
201
,
202
, and
203
provide “hard decision” data to the base station controller
207
. The “hard decision” data represent a determination by the base station as to what the final received data are. The “hard decision” data are independent of the metric signal and are independent of the “hard decision” data provided to the base station controller
207
by other base stations. Since the “hard decision” data involve a decision being made at a base station as to what the final received data are, the base station controller is merely able to select “hard decision” data from among that provided by the base stations.
The presence of multiple independent receivers provides what is referred to as diversity in receiving the reverse link signal from the mobile unit. The type of diversity where the base station controller
207
simply chooses the frame of data from the base station with the largest metric signal is referred to as selection diversity.
The receivers
204
,
205
, and
206
are independent receivers in that they are geographically separate from each other and they provide data over relatively low bandwidth links to a common location. The limited bandwidth of the links imposes some constraints on the manner in which the data are communicated.
One problem with the techniques relates to the difficulty of determining a signal-to-noise ratio of the signal carrying the data. The signal-to-noise ratio affects the likelihood that the data will be correctly interpreted. However, no information about the signal-to-noise ratio is typically transmitted from a base station to the base station controller. Consequently, no provision is made at the base station to determine the signal-to-noise ratio.
Even if circuits were added to a base station to determine the signal-to-noise ratio, such circuit would increase the cost and complexity of each base station in which they were used. With cell sizes being reduced and the number of base stations increasing, such additional cost and complexity of each base station would greatly increase the overall system cost. Moreover, even if such circ
Agami Gregory
Corke Robert J.
Rotstein Ron
Ghayour Mohammad
Motorola Inc.
Pace Lalita W.
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