Wireless communication apparatus which communicates at specified frame cycles

A method is provided for selecting multiple customer premises equipments (CPEs) to share a channel in a wireless communications network. The method includes calculating a correlation between spatial signatures of every two CPEs subscribing to a base transceiver station (BTS) of the wireless communications network, wherein two CPEs constitute channel-sharing candidates if their correlation is lower than a predetermined threshold, creating a first set of CPEs of all the member of channel-sharing candidates, counting a number of channel-sharing candidates a CPE relates to for every CPE, selecting a first CPE related to the fewest number of channel-sharing candidates, creating a second set of CPEs by identifying all the CPEs that the first CPE relates to, and selecting a second CPE related to the fewest number of channel-sharing candidates from the second set of CPEs, wherein the first and second CPEs become two selected CPEs to share the channel.

BACKGROUND

Spatial division multiple access (SDMA) increases the capacity of a wireless communications network by allowing more than one wireless station to access a communication channel on the same frequency at the same time. One example of channel sharing is that wireless stations, such as customer premises equipments (CPEs), transmit signals on the same frequency at different times or on different frequencies at the same time.

How to select a set of CPEs to share a communication channel is a very complicated and computationally intensive process. This is true primarily because not every CPE can share a communication channel with other CPEs in a wireless communications network employing SDMA.

There are a number of reasons why some CPEs cannot share a communication channel. One of the reasons is co-channel interference (CCI), which occurs when a CPE receives unintended signals from other CPEs sharing the same communication channel. This type of inter-user interference is the major drawback of an SDMA system. To suppress inter-user interference, an SDMA system must provide a means to isolate the spatial signatures of one CPE from those of the rest of the CPEs sharing a channel. Otherwise, inter-user interference may cause a communication channel to be unusable for the entire set of CPEs.

A second reason is that different CPEs may subscribe to the services of a base transceiver station (BTS) at any given time. In other words, a set of CPEs sharing a communication channel at one point in time may not be the same set of CPEs sharing the same communication channel at another time. A third reason is that the characteristics of the radio link may change over time.

In a conventional method, a BTS selects an optimal set of CPEs to permanently share a communication channel in a wireless communications network employing SDMA, based on certain predetermined parameters. The optimal set of CPEs chosen to share a communication channel at one time might not be optimal at a later time. Therefore, the permanent grouping of CPEs to share a communication channel is ineffective and inefficient.

What is desired is a system and method for improving the grouping of CPEs dynamically in a wireless communications network employing SDMA that addresses the dynamic nature of the radio link and participants of communication sessions.

SUMMARY

A method is provided for selecting multiple customer premises equipments (CPEs) to share a channel in a wireless communications network. The method comprises calculating a correlation between spatial signatures of every two CPEs subscribing to a base transceiver station (BTS) of the wireless communications network, wherein two CPEs constitute channel-sharing candidates if their correlation is lower than a predetermined threshold, creating a first set of CPEs of all the members of channel-sharing candidates, counting a number of channel-sharing candidates a CPE relates to for every CPE, selecting a first CPE related to the fewest number of channel-sharing candidates, creating a second set of CPEs by identifying all the CPEs that the first CPE relates to, and selecting a second CPE related to the fewest number of channel-sharing candidates from the second set of CPEs, wherein the first and second CPEs become two selected CPEs to share the channel.

The construction and method of operation of the techniques described herein, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

DESCRIPTION

The following detailed description refers to the accompanying drawings. The description includes exemplary embodiments, not excluding other embodiments, and changes may be made to the embodiments described without departing from the spirit and scope of the subject matter described herein.

The method and system described herein reduces inter-user interference and improves the bit error rate (BER) for a group of CPEs in a wireless communications network employing SDMA. The selection of a group of CPEs to share a communication channel is based on the isolation of spatial signatures and path loss differences. The method and system described herein is applicable to any wireless communications network and the term channel refers to any of the conventional multiple access channels such as frequency, time, code or any combination of them. The method can be extended to include more than two CPEs, though the techniques described herein are directed to how to select two CPEs to share a communication channel.

With reference toFIG. 1, a wireless communication network5is shown comprising a base transceiver station (BTS)10and multiple customer premises equipments (CPEs) C1-CK. The CPEs C1-CKwirelessly communicate with the BTS10. Assume that there are K CPEs that subscribe to the services of the BTS10in a cell of the wireless communications network5employing SDMA. By using the method described herein, the BTS10dynamically decides which CPEs would share a communication channel.

FIG. 2is a flow diagram illustrating a method to have a channel shared by two CPEs based on the isolation of spatial signatures.

Let {C1, C2, . . . , CK} denote the set of K CPEs subscribing to the services of the BTS equipped with M antennas. Let the spatial signature of CPE Cibe denoted as

hi=[hi,1hi,2⋮hi,M],
where m ∈(1,2, . . . ,M) and hi,mis a spatial signature associated with antenna m.

Each CPE Ciis a candidate for sharing a communication channel with another CPE Cj. A partner set χCi, which includes all the CPEs that could share a communication channel with the CPE Ci, is created for each CPE Ci. The number of CPEs in the set χCiis denoted as nCi. A number set, denoted as χpre—number={nC1, nC2, . . . , nCk}, is formed to show the number of partners of each CPE Ci.

In step110, for each Cj, where 1≦j≦K and i≠j, the correlation sijbetween CPE Ciand CPE Cjis calculated according to the following equation:

sij=hiH⁢hj=∑m=1M⁢hi,m*⁢hj,m.⁢(…)H
denotes a Hermitian operator. If sijγ0, where γ0is a predetermined threshold and 0≦γ0≦1, then Cjis included in the partner set χCiof CPE Ci.

The number of CPEs in the partner set of CPE Ciis denoted as nCi. If nCi>0, Ciis included in a set χpre, i.e., χpre=χpre∪{Ci} and nCiis included in the χpre—number. The set χprecontains the CPEs that are pre-qualified to share a communication channel with another CPE. Step110is repeated for every CPE in the set {C1, C2, . . . , CK}.

In Step120, the smallest element of χpre—numberis selected. If more than one nCihas the same smallest value, a predetermined tie-breaker rule is employed to select only one nCi. For example, the first one of at least two CPEs that have the same smallest number in the χpre—numberis selected. In other words, CPE Ciwith the smallest number of partners is chosen to be one of the two CPEs selected to share a communication channel.

In step130, let χpeer=χCj. For each CPE Cjin the χpeer, the partner set of Ci, nCjis included in the set χpeer—number.

In step140, the smallest element of χpeer—numberis selected. If more than one nCjhas the same smallest value, a predetermined tie-breaker rule is employed to select only one nCj. In other words, CPE Cjwith the smallest number of partners, is chosen to be the other CPE that is to share a communication channel. A pair of CPEs (Ci, Cj) is identified to share a communication channel.

In Step150, CPEs Ciand Cjare removed from the χpre; nCiand nCjare removed from the χpeer—number. If there is more than one element in χpre, the pairing process repeats from step120. The process continues until no more CPEs could share a communication channel. All feasible CPE pairs in SDMA are identified.

FIG. 3illustrates a second method to have a channel shared by two CPEs based on the isolation of spatial signatures and path loss.

Let {C1, C2, . . . , CK} denote the set of K CPEs subscribing to the services of the BTS equipped with M antennas. Let the spatial signature of CPE Cibe denoted as

hi=[hi,1hi,2⋮hi,M],
where m ∈(1,2, . . . ,M) and hi,mis a spatial signature associated with antenna m. Let αidenote the path loss of CPE Ci. Each CPE Ciis a candidate for sharing a communication channel with another CPE Cj.

Two predetermined thresholds γ1and Δγ, where 0≦γ1≦1 and 0≦Δγ≦γ1, are chosen. The Δγ is the marginal threshold of γ1. A good guideline for the selection of Δγ is 0.1γ1≦Δγ≦0.2γ1.

In Step210, for each Ci, where 1≦i≦K, if αi≧γ1+Δγ, then CPE Ciis included in the set χpre, i.e., χpre=χpre∪{Ci}. Let L denote the number of CPEs with a path loss that satisfies the above condition.

In step220, CPE Ciwith the smallest αiis selected to be one of the two CPEs to share a communication channel. If more than one CPE has the same smallest path loss, a predetermined tie-breaker rule is employed to select only one. For example, the first of the CPEs that have the smallest path loss is selected.

In step230, for each Cjin the χpre, where 1≦j≦L and i≠j, the correlation sijbetween CPE Ciand CPE Cjis calculated according to the following equation:

sij=hiH⁢hj=∑m=1M⁢hi,m*⁢hj,m.⁢(…)H
denotes a Hermitian operator. CPE Cjthat has the smallest correlation with CPE Ciis identified to be a potential partner.

In step240, for CPEs Ciand Cj, a value based on spatial signatures and path loss is calculated according to the following equation: αi(1−|hiHhj|2).

In step250, if αi(1−|hiHhj|2)≧γ1, then CPE Cjis the other CPE that is to share a communication channel. A pair of CPEs (Ci, Cj) is identified to share a communication channel and then CPEs Ciand Cjare removed from the set χpre.

If αi(1−|hiHhj|2)<γ1, CPE C1cannot be the one to share a communication channel with CPE Cj. CPE Ciis then removed from the set χpre. If more than one CPE remains in the set χpre, the selection process is repeated from step220.

The process continues until no two CPEs could share a communication channel. All pairs of CPEs that could share a communication channel in SDMA are identified.

The above illustration provides many different embodiments or embodiments for implementing different features of the subject matter described herein. Specific embodiments of components and processes are described to help clarify the subject matter described herein. These are, of course, merely embodiments and are not intended to limit the subject matter described herein.