Communications: radio wave antennas – Antennas – Plural antennas
Reexamination Certificate
2001-01-10
2002-04-30
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Plural antennas
C343S702000
Reexamination Certificate
active
06380910
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to wireless devices comprising a cluster of antennas coupled to a signal processing device and a method of constructing such devices.
2. Description of the Related Art
One of the more critical pieces of equipment in a communication network and, in particular, in a wireless communication network is the antenna. Antennas are used to convey information (i.e., transmit and receive information) in the form of electromagnetic waves over communication links of a network.
The owners and/or operators of communication networks, i.e., the service providers, are constantly searching for methods and equipment that can meet the changing needs of their subscribers. Subscribers of communication networks, including wireless communication networks, require higher information throughput in order to exploit the expanding range of services being provided by current communication networks. For example, wireless communication subscribers are now able to have simultaneous access to data networks such as the Internet and to telephony networks such as the Public Switched Telephone Network (PSTN). Also, service providers are constantly investigating new techniques that would allow them to increase their information transfer rate. Information transfer rate is the amount of information—usually measured in bits per second—successfully conveyed over a communication channel. The information transfer rate can be increased in a number of well known manners. One way is by increasing the power of the transmitted signals. A second way is by expanding the frequency range (i.e., bandwidth) over which the communication is established. However, both power and bandwidth are limited by certain entities such as governmental and standards organizations that regulate such factors. In addition, for portable devices, power is limited by battery life.
An approach that circumvents the power and bandwidth limitations is to increase the number of antennas used to transmit and receive communication signals. Typically, the antennas are arranged as an array of antennas. Three of the more general ways of using antenna arrays are (a) phased array applications, (b) spatial diversity techniques (c) space-time transmit diversity techniques as well as (d) more general Multiple Input Multiple Output (MIMO) techniques. A phased array comprises an antenna array coupled to a device, which controls the relative phase of the signal in each antenna in order to form a focused beam in a particular direction in space. Spatial diversity is the selection of a particular antenna or a group of antennas from an array of antennas so as to transmit or receive signals in order to improve information throughput. In a spatially diverse structure the antenna array is typically coupled to a receive diversity device that utilizes one of many combining techniques, such as Maximum Ratio Combining, switching, or other combining techniques well known to those skilled in the art. Unlike phased arrays and spatial diversity techniques wherein one or a group of antennas are used to transmit or receive a single signal, space-time transmit diversity and MIMO techniques use an antenna array coupled to a signal processing device to simultaneously transmit and/or receive multiple distinct signals. Space-time transmit diversity coding (STTD) uses two or more transmitting antennas in order to take advantage of both the spatial and temporal diversity of the channel; WCDMA for UMTS, p. 97, ed., H. Holma & A. Toskala.
One of the main features of MIMO systems is that they benefit from the multipath propagation of radio signals. In a multipath environment, radio waves transmitted by an antenna do not propagate in straight lines towards the receive antenna. Rather, the radio waves scatter off a multitude of objects that block the direct path of propagation. Thus, the environment creates a multitude of possible paths from transmit to receive antennas. These multiple paths interfere with each other at the location of the receive antenna. This interference process creates a pattern of maxima and minima of received power, with the typical spatial separation between consecutive maxima being approximately one wavelength. MIMO systems exploit the rich scattering environment, and use multiple transmitters and receivers to create, in effect, a plurality of parallel subchannels each of which carries independent information. For transmitting antennas, the transmitted signals occupy the same bandwidth simultaneously and thus spectral efficiency is roughly proportional to the number of subchannels. For receiving antennas, MIMO systems use a combination of linear and nonlinear detection techniques to disentangle the mutually interfering signals. Theoretically, the richer the scattering, the more subchannels that can be supported.
While MIMO techniques theoretically allow antenna arrays to have relatively high information rates, the actual achieved information transfer rate will greatly depend on how the information is coded in the different subchannels. An example of how a MIMO system can be implemented is the BLAST (Bell Labs LAyered Space Time) scheme conceived by Lucent Technologics headquartered in Murray Hill, N.J. There are several realizations of the general BLAST architecture. One of them is known as diagonal-BLAST, or D-BLAST, proposed by G. J. Foschini and M. Gans,
Wireless Commun.
6, 311 (1998). Another alternative includes vertical-BLAST, or V-BLAST (proposed by G. D. Golden, G. J. Foschini, R. A. Valenzuela, and P. W. Wolniansky,
Electronic Letters
35, 14 (1999)). These implementations can reach a significant (above 80%) fraction of the theoretical information transfer rate expected for rich scattering environments.
As with the idealized MIMO case, in all BLAST implementations the information transfer rate of the system increases as the number of antennas in a transmit and/or receive array is increased. However, in many cases the amount of space available for the antenna array is limited. In particular, the space limitation is very critical for portable wireless devices (e.g., cell phones, Personal Digital Assistants (PDA)). Increasing the number of antennas in an array of limited space decreases the spacing between individual antennas in the array. The reduced spacing between antennas typically causes signal correlation to occur between signals received from different antennas. Signal correlation reduces the gain in information transfer rate obtained by the use of MIMO techniques; A. L. Moustakas et al.,
Science
287, 287 (2000).
Correlation is quantitatively defined in terms of at least two signals. When any two signals s
1
(t) and s
2
(t) are being transmitted or received, the degree of correlation between these two signals is given by the absolute value of the following expression:
∫
t
1
t
2
s
1
(
t
)
s
2
(
t
)
*
ⅆ
t
∫
t
1
t
2
&LeftBracketingBar;
s
1
(
t
)
&RightBracketingBar;
2
ⅆ
t
∫
t
1
t
2
&LeftBracketingBar;
s
2
(
t
)
&RightBracketingBar;
2
ⅆ
t
where s
2
*(t) corresponds to the complex conjugate of s
2
(t) and t
1
and t
2
are times selected in accordance to rules well known to those skilled in the pertinent art. When two signals have a relatively low correlation or are uncorrelated, the above integral becomes relatively small.
In particular, received signal correlation is a phenomenon whereby the variations in the parameters (i.e., amplitude and phase) of a first signal of a first antenna track the variations in the parameters of a second signal of a second antenna in the vicinity of the first antenna;
Microwave Mobile Communications
, W. J. Jakes (ed.), chapter 1, IEEE Press, New York (1974). Also, the correlation between received signals can be determined by the correlation of the radiation patterns of the antennas receiving the signals. As is known to those skilled in the art, the radiation pattern of a particular antenna is the relative
Moustakas Aris L
Safar Hugo F
Simon Steven H
Stoytchev Marin
Lucent Technologies - Inc.
Narcisse Claude R.
Nguyen Hoang
Wong Don
LandOfFree
Wireless communications device having a compact antenna cluster does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wireless communications device having a compact antenna cluster, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wireless communications device having a compact antenna cluster will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2922271