Patent Application
20080136735
The present invention relates generally to wireless communications, and more particularly to a method for partitioning antenna array in a wireless communication system.
It has become increasingly common for wireless communication systems to equip with a plurality of antennas in order to improve signal coverage and increase system reliability. Beam forming (BF) is one of the transmission schemes that are broadly used, due to its reliability against signal fading. BF is a technique used with arrays of transmitters or receivers that controls a radiation pattern. When receiving a signal, BF can increase the gain in the direction of wanted signals and decrease the gain in the direction of interference and noise. When transmitting a signal, a beamformer controls the amplitude and phase of the signal at each transmitter, in order to create a constructive pattern in a desired direction. As such, information from different sensors can be combined in a way that an expected pattern of radiation can be observed.
Recently, space-time coding (STC) has attracted many attentions in the wireless communication industry. STC relies on transmitting multiple, redundant copies of a data stream to the receiver in order to increase their change of surviving a physical path between transmission and reception, and still remain in a good enough state for reliable decoding. Similar to BF, STC improves reliability against short-term fading.
Depending on various wireless network parameters, it is sometimes advantageous to employ BF and STC simultaneously in an antenna array. This usually requires partitioning the antenna array, where each partition represents a virtual antenna, such that STC can be implemented among various virtual antennas and BF can be performed by each virtual antenna.
In order to improve the performance of an antenna array implemented with both BF and STC schemes, spatial correlations among these virtual antennas should be low. Besides physical deployments of the antennas, the spatial correlations depend on various factors, mainly the signal propagation environment. Thus, before partitioning an antenna array, its spatial correlations must be obtained through some training, or blind approaches.
Conventionally, it is usually difficult to provide a partitioning scheme, which offers good performance throughout a long time span. This is due to the fact that statistical properties of a wireless channel between an antenna array and a wireless node can change in a way that a partitioning scheme is favorable in a given time and unfavorable in another. For example, with reference to
As such, what is needed is a method for partitioning a plurality of antennas in a wireless communication system using both BC and STC in a way that mitigates the impact a change of channel conditions makes on signal transmission.
The present invention discloses a method for partitioning a plurality of antennas in a wireless communication system. In one exemplar method, the antennas are grouped into a first set of partitions and a second set of partitions. One or more signal transmission schemes are performed with the antennas grouped into the first set of partitions for a first time period, and then with the antennas grouped into the second set of partitions for a second time period.
The construction and method of operation of the invention, however, together with additional objectives and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
This invention describes a method for partitioning an antenna array in a wireless communication system. The following merely illustrates various embodiments of the present invention for purposes of explaining the principles thereof. It is understood that those skilled in the art will be able to devise various equivalents that, even though not explicitly described herein, embody the principles of this invention.
The antennas N11, N12, N13 and N14 can be grouped into more than one set of antenna partitions. For example, antennas N11 and N13 can also be grouped into a partition, and antennas N12 and N14 into another. These partitions are collectively referred to as the second set of antenna partitions. In this embodiment, BF and STC schemes are performed based on the first set of antenna partitions for a first predetermined time period. Upon expiration of the first time period, the wireless communication system switches to use the second set of antenna partitions for a second predetermined time period. This process is repeated by hopping between the two sets of antenna partitions. Thus, when a change of conditions of a wireless channel causes a virtual antenna to function ineffectively or inefficiently, the antenna partition hopping can provide the virtual antenna with various combinations of physical antennas over a long period time, thereby avoiding a permanent failure of this particular virtual antenna.
It is noted that the numbers of antennas for two partitions do not have to be the same. Neither do the antennas within one partition needs to be physically adjacent to one another, event though their spatial correlations should be low. It is also noted that hardware implications of this portion hopping scheme is negligible since both STC and BF are fully implemented in the digital signal processing (DSP) level.
The above mentioned partition hopping scheme can be expanded to a wireless communication system having N antennas at the signal transmitting end. Assuming that STC utilizes a two-antenna orthogonal black, it would suffice to partition the antenna array into two partitions, each with one half of physical antennas, i.e., N/2. T sets of antenna partitions {P1, P2 . . . Pt} are selected randomly or pseudo-randomly for T time periods {t1, t2 . . . tT}, during each of which its corresponding set of antenna partitions is used for performing BF and STC. For example, as shown in
It is noted that the sequence {P1, P2 . . . Pt} may be different from one wireless node to another. It is noted that although, in the above example, the antenna partitions are selected randomly or pseudo-randomly, they can also be selected according to a predetermined pattern or order. For example in a wireless communication system where N physical antennas are to be grouped into two partitions, one partition can be made from the odd number antennas and the other partition can be made from the even number antennas.
The proposed partition hopping scheme can be applied in a wireless communication system that uses orthogonal frequency-division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA) technology.
The above mentioned partitioning scheme can be expanded to a wireless communication system having N antennas at the signal transmitting end. In a wireless communication system using OFDM/OFDMA technology, a channel can be divided into slots defined by time periods {t1, t2 . . . tT} multiplied by subcarriers {π1, π2 . . . πF} where T is the number of time slots and F is the number of subcarriers. The multiple sets of antenna partitions are defined as a T×F matrix, {[P1,1 . . . P1,F] . . . [PT,1 . . . PT,F]}.
One advantage of the proposed antenna partition hopping scheme is to reduce the impact caused by a change of signal propagation environment on a wireless communication system, without having to acquire statistical knowledge of wireless channels. Since the conditions of wireless channels change overtime, conventional fixed partition schemes may not be proper, and therefore may cause degradation of system performance. Furthermore, the proposed antenna partition hopping scheme allows a wireless communication system to be built in a cost-efficient way, since acquiring statistical knowledge of a wireless channel in order to compensate a change of channel conditions often requires additional complex hardware or software implementations.
The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims.
Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims.
The present application claims the benefits of U.S. Provisional Patent Application Ser. No. 60/837,981, which was filed on Aug. 15, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60837981 | Aug 2006 | US |
