Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2001-07-30
2004-08-17
Maung, Nay (Department: 2684)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S328000, C370S327000, C370S341000, C370S310200, C370S442000, C370S432000, C370S458000
Reexamination Certificate
active
06778513
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of wireless communications systems, and in particular, to a method and system for separating and/or distinguishing between signals associated with multiple remote user terminals occupying the same channel.
BACKGROUND OF THE INVENTION
One advance in increasing the capacity of communication systems has been in the area of resource sharing or multiple access. Examples of multiple access techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), and time division multiple access (TDMA). For example, in a TDMA system, each remote user terminals communicates with a hub communication device (e.g., a base station) in a frequency channel shared with other remote user terminals, but in its own (i.e., non-overlapping) time slot. As such, in a TDMA system, multiple remote user terminals may communicate with the hub communication device within the same frequency channel, but within non-overlapping time slots. (The term “channel” as used herein refers to any one or a combination of conventional communication channels, such as frequency, time, code channels).
Typically, a wireless communication network will include a number of hub communication devices distributed over a geographic region to service several remote user terminals, as well as to allow the same channels to be reused. For example, in voice and/or data cellular communication networks, the same channel may be used by more than one hub communication device if the possibility of interference is limited, for example, due to geographic separation of hubs occupying the same channel(s) or geographic obstructions. Generally, there is a trade-off between channel reuse and capacity of remote user terminals that can be accommodated in a wireless communication network.
Although antennas have sometimes been one of the neglected components of wireless systems, relatively recent development in the field of (adaptive) antenna arrays and “smart antennas” have not only realized significant improvements in geographic capacity, but also in signal-to-noise ratio (SNR), interference reduction, directionality, spatial diversity, power efficiency, and security. Accordingly, employment of antenna arrays has been proposed in a number of different wireless applications, including, but not limited to, radio communication systems, cellular systems, television broadcasting, paging systems, medical applications, etc.
Antenna arrays typically include a number of antennas that are spatially separated and coupled to one or more processors. Adaptive antenna arrays, or simply, adaptive arrays, periodically analyze the signals received from each of the antennas in an array to distinguish between one or more desired signals (e.g., from a desired source, such as cellular telephone or other communication device) and one or more undesired signals (e.g., interference from users of other hubs sharing the same frequency, interference from other radio frequency (RF) emissions overlapping in channel, Johnson noise, multipath, or other interference sources, etc. Because adaptive array systems may sometimes be able to distinguish between spatially distinct sources (e.g., two cellular user units at different locations), such systems are sometimes referred to as “spatial processing” or “spatial division multiple access (SDMA)” systems. In general, adaptive array systems provide relatively significant improvement in performance relative to single antenna element systems.
FIG. 1A
is a diagram depicting a simplified radiation pattern of an antenna array system, according to the prior art. In the system shown in
FIG. 1A
, an antenna array
10
transmits (downlink) signals to and/or receives (uplink) signals from a desired source
12
, such as a mobile or stationary remote user terminal (e.g., a cellular voice and/or data communication device, a PDA having wireless capability, etc.). As shown, a beamforming pattern
8
, which represents the transmission and/or reception directional gain pattern (depicted for only two dimensions) for the antenna array
10
, includes a region of enhanced gain
6
, as well as a region of relatively minimized gain or “null” region
2
and another region of relatively minimized gain or null
4
.
The null regions
2
and
4
represent one of the advantages of adaptive arrays and “smart antenna” processing. In particular, each of the nulls
2
and
4
represent a represent a region or direction of relatively minimized gain with respect to the beamforming pattern of the antenna array
10
. As such, the antenna array
10
typically directs a null in the direction of an interfering source. To this end, the null
2
is directed toward an interfering source
14
, while the null
4
is directed to the interfering source
16
. The interfering sources
14
and
16
each may represent a moving car, another mobile or stationary remote user terminal in communication with the antenna array
10
or another communication device (e.g., a base station that may or may not include an antenna array), etc., which may cause interference. As such, null generation may be viewed as interference mitigation, and each “null region” may be referred to as an interference mitigated region.
By enhancing the gain in the direction of desired source, while diminishing (and ideally reducing to zero) the gain in the direction of one or more interfering sources, the antenna array
10
may “directionally” receive and transmit signals, and as such, increase system capacity, decrease interference to the desired source(s), etc.
FIG. 1B
is a graphical representation of a beamforming pattern for the antenna array
10
shown in
FIG. 1A
, according to the prior art. In
FIG. 1B
, the level of the transmission (downlink) and reception (uplink) gain of the antenna array
10
is depicted on the vertical axis and (spatial) direction is shown on the horizontal axis. As shown, there is relatively greater gain in the direction of the desired source
12
, which corresponds to the enhanced gain region
6
, than there is toward the interfering source
14
, which corresponds to the null region
2
, or the interfering source
16
, which corresponds to the null region
4
.
It should be appreciated that the term “null” as used in the context of adaptive array systems does not necessarily mean, and often does not mean, a region of zero electromagnetic energy, since nulls may often include some level of gain, though typically less than the enhanced region
6
. Ideally, a communication device employing an adaptive array would direct a null having zero gain toward an interfering source. Furthermore, the closer the gain value of a null is to zero, the more intense or “deep” the null is. Thus, the “amount of nulling” that an antenna array or adaptive array system may generate may be defined one or both the number of nulls and the intensity of such nulls, such that the greater the amount of nulling, the greater the number of nulls generated and/or the more intense/deep one or more nulls are. As shown in
FIG. 1B
, for example, the null
2
is less intense than the null
4
, since the latter represents less gain (and greater nulling intensity).
Regardless of the type of communication system or multiple access technology, a “hub” communications device, such as a base station or portion thereof, generally should be able to: (1) sufficiently recover the desired signal from all the signals received on a given channel; and (2) determine the identity of the source of each desired signal. For example, in a cellular communication system that includes a number of base stations each acting as a hub, when two or more remote user terminals are communicating with their corresponding hubs on the same reused channels, each cellular base station should be able to perform steps (1) and (2) for each signal or set of signals associated with a particular “desired” remote user terminal, while discarding the signal(s) associated with interfering sources.
In a spatial processing system, wherein the hub communication device may be part
Barratt Craig H.
Kasapi Athanasios A.
Parrish David M.
Trott Mitchell D.
ArrayComm, Inc.
Maung Nay
Sharma Sujatha
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