METHOD FOR PERFORMING WIRELESS SWITCHING

Abstract

A wireless communication system includes an infrastructure device for transmitting and receiving communications to and from a plurality of wireless user terminals. Each wireless user terminal includes a receiver and a controller configured to receive a plurality of orthogonal frequency division multiplexing (OFDM) signals on at least one downlink carrier frequency. Each of the plurality of OFDM signals includes assignment information. The receiver is configured to receive a plurality of downlink signals each responsive to a respective OFDM signal of the plurality of OFDM signals such that each downlink signal is received on a downlink carrier frequency and using a downlink spatial pattern. Further, the controller is configured to dynamically change the downlink carrier frequency of the receiver for receiving the plurality of downlink signals based on the plurality of OFDM signals, wherein the plurality of downlink signals have different spatial patterns.

Description

FIELD OF INVENTION

The present invention relates to a Wireless LAN system (WLAN) with several users connected. More particularly, switching of WLAN systems for avoiding collisions.

BACKGROUND

WLAN systems make use of the unlicensed bands for wireless communication. Transmissions of a wireless LAN (WLAN) communication system may be from a particular terminal to a desired destination, either another terminal within the same Basic Service System (BSS) or the backbone network, but always within the same carrier. There are two modes of operation for WLAN systems: ad-hoc and infrastructure. In the ad-hoc mode, terminals can talk to each other in a multipoint-to-multipoint fashion. In the infrastructure mode, an access point (AP) acts as a base station to control the transmissions among users, thus providing a point-to-multipoint wireless network. Since all the users share the same medium in a WLAN, the infrastructure mode becomes more efficient for semi-heavy to heavy loaded networks.

In an infrastructure mode, the terminal first communicates with the AP when sending data to a desired destination terminal. The AP in turn bridges or routes the information to the desired destination. Thus, in this mode, an AP of a WLAN communication system controls the transmissions within a BSS or cell.

Medium Access Control (MAC) protocols are defined to coordinate the channel usage for WLAN users sharing the band. These MAC protocols are based upon avoiding collisions between users as several users access the channel at the same time. The efficiency of a protocol is gauged by successful avoidance of collisions.

Two protocols used by WLAN are CSMA/CA MAC and CSMA/CD Ethernet protocol. Both protocols can sense the carrier for other transmissions. An Ethernet can be connected in various manners, including Ethernet hubs and Ethernet switches. An Ethernet hub concentrates the connections in a central point as a point-to-multipoint connection, with no impact on performance. An Ethernet switch operates every time that there is a packet arrival from a terminal. The switch reads the destination address, learns on which port it is connected and makes a direct connection between the two physical ports. The advantage of the Ethernet switch is that the MAC does not sense any other user in the medium, which improves performance through reduced probability of collisions and enhanced throughput as compared to an Ethernet hub. An Ethernet hub forwards a received packet to all users, even when there is only one intended receiver. The hub does not look at address information. The Ethernet switch only sends the packet directly to the intended destination, resulting in a more efficient usage of the available bandwidth.

A common WLAN AP is not capable of using more than one carrier frequency at the same time, which results in low protocol efficiency. Ethernet switches have proven to improve the efficiency of the Ethernet protocol considerably.

Therefore, what is needed is a method for improving the performance of a wireless point-to-multipoint network when the terminals share the same medium.

SUMMARY

A wireless communication system includes an infrastructure device for transmitting and receiving communications to and from a plurality of wireless user terminals. Each wireless user terminal includes a receiver and a controller that receives a plurality of orthogonal frequency division multiplexing (OFDM) signals on a first carrier frequency of a downlink. Each of the plurality of OFDM signals includes carrier frequency assignment information indicating a carrier frequency to transmit uplink data and spatial pattern information indicating a spatial pattern. In response to the carrier frequency assignment information of each of the plurality of OFDM signals, a transmitter and the controller of the wireless user terminal transmit a plurality of uplink signals. Each of the plurality of uplink signals are transmitted on the indicated carrier frequency and using the indicated spatial pattern.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1A shows a system diagram of a WLAN with frequency carrier Ethernet ports.

FIG. 1B shows a simplified diagram of a user terminal and a switching access point using frequency carrier Ethernet ports.

FIG. 2A shows a system diagram of a WLAN with spatial beam Ethernet ports.

FIG. 2B shows a simplified diagram of a user terminal and a switching access point using spatial beam Ethernet ports.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A shows a system that applies the Ethernet switch principle to an access point (AP), allowing multi-frequency operation, so that the AP becomes a Switching Access Point (SAP) 106. Frequency carriers f1-f5 are treated as different ports in the SAP, from which user terminals 101-105 have centralized access to frequency carriers f1-f5 in a controlled manner.

As shown in FIG. 1A, each user terminal 101-105 is assigned to a frequency carrier f1-f5 and SAP 106 is capable of receiving and transmitting each carrier f1-f5. In order to avoid permanent assignment of carriers f1-f5 to each user terminal 101-105, two approaches may be used. In the preferred embodiment, it is desirable, although not essential, to not permanently assign carriers to user terminals 101-105. A non-permanent assignment avoids assigning a frequency to a terminal not sending data. When there are more terminals than available frequencies, a terminal that has data to send can be prevented from doing so if the terminal permanently assigned to a frequency is not using it.

A dynamic carrier assignation (DCA) scheme can be applied, in which user terminals 101-105 send a request-to-send (RTS) in a shared carrier and then the SAP replies with a clear-to-send (CTS) indicating the carrier that can be used for the transmission.

Alternatively, a frequency hopping scheme may be used, in which user terminals 101-105 have a pseudo-random sequence for changing carriers, known a priori by user terminals 101-105 and SAP 106, to minimize the probability of two user terminals simultaneously using the same carrier. For a preferred WLAN developed according to the current 802.11b standard, three carriers are used for frequency hopping. For the 802.11a standard, eight carriers are used for frequency hopping. Wireless switching system 100 may employ DCA and frequency hopping either separately or combined.

FIG. 1B is an illustration of a preferred user terminal and SAP using multiple frequencies. The SAP 106 has a frequency assignment device 120 for assigning frequencies (frequency ports) to the user terminals 101-105. A multiple frequency receiver 118 receives data sent by the terminals 101-105 using the assigned frequency port. A multiple frequency transmitter 116 sends data from one terminal to another using the assigned frequency of the destination terminal. The multiple frequency transmitter 116 preferably also transmits the frequency assignment to the terminals 101-105. An antenna 122 or antenna array is used to send and receive data by the SAP 106 over the wireless interface 124.

The terminals 101-105 have a multiple frequency receiver 114 for receiving the frequency assignment and recovers the transmitted data over the terminal's assigned frequency. A frequency controller 108 users the received assigned frequencies to control the transmission and reception frequencies of the terminal 101-105. A multiple frequency transmitter 110 transmits the data over the assigned frequency.

FIG. 2A shows an alternative embodiment of wireless switching by assigning each user terminal 201-205 to a spatial port instead of a particular frequency. As shown in FIG. 2A, spatial beams b1-b5 are created by beam forming and can be used as ports to isolate user terminals 201-206 from each other. SAP 206 recognizes the destination address of each user terminal 201-205, and associates a beam to each address. SAP 206 is capable of receiving more than one beam at the same time.

FIG. 2B is an illustration of a preferred user terminal and SAP using spatial beams. The SAP 206 has a beam controller 220 for determining which beam (spatial port) is associated with a particular user. The controller 220 provides a beam forming transmitter 216 and a beam forming receiver 218 the beam information so that the appropriate spatial port is used for a given terminal. An antenna array 214 is used to send and receive data over the wireless interface 222.

The terminals 201-205 have a beam forming receiver 210 for receiving transmitted data using an antenna array 212. A beam forming transmitter 208 is used to transmit data to the SAP 206 using the array 212.

Although the system configurations of FIGS. 1A, 1B, 2A and 2B show five user terminals, any number of user terminals may be used. The intent is to demonstrate and not to limit or restrict the scope of the system capabilities. The wireless switching systems of FIGS. 1A and 2A can be used separately or combined. To illustrate, user terminals 101-105 can be distinguished by a combination of spatial beam and frequency. The wireless switching systems of FIGS. 1A and 2A can be applied to systems including, but not limited to, direct sequence (DS) WLAN and orthogonal frequency division multiplexing (OFDM) WLAN systems.

Claims

1. A wireless user terminal comprising: a plurality of antennas and a receiver configured to receive a first plurality of downlink orthogonal frequency division multiplexing (OFDM) signals on at least one downlink carrier frequency, wherein each of the first plurality of downlink OFDM signals includes assignment information; andthe plurality of antennas, the receiver and a controller is further configured to receive a second plurality of downlink OFDM signals, wherein each of the second plurality of downlink OFDM signals is received based on the assignment information in a respective one of the first plurality of downlink OFDM signals; wherein a downlink carrier frequency and a downlink beam dynamically change over the second plurality of downlink OFDM signals; wherein at least two of the second plurality of downlink signals have different downlink carrier frequencies and at least two of the second plurality of downlink signals have different downlink beams.

2. The wireless user terminal of claim 1 wherein each assignment information indicates the downlink carrier frequency of a respective one of the second plurality of OFDM signals.

3. The wireless user terminal of claim 1 wherein each downlink carrier frequency comprises a mutually non-overlapping band of sub-carriers.

4. The wireless user terminal of claim 1 further comprising a transmitter, wherein the plurality of antennas, the transmitter and the controller are configured to transmit a plurality of uplink OFDM signals using at least two different uplink beams.

5. The wireless user terminal of claim 1 further comprising a transmitter, wherein the plurality of antennas, the transmitter and the controller are configured to transmit a plurality of uplink OFDM signals using at least two different uplink carriers based on received uplink channel assignment information.

6. A method comprising: receiving, by a wireless user terminal, a first plurality of downlink orthogonal frequency division multiplexing (OFDM) signals on at least one downlink carrier frequency, wherein each of the first plurality of downlink OFDM signals includes assignment information; andreceiving, by the wireless user terminal, a second plurality of downlink OFDM signals, wherein each of the second plurality of downlink OFDM signals is received based on the assignment information in a respective one of the first plurality of downlink OFDM signals; wherein a downlink carrier frequency and a downlink beam dynamically change over the second plurality of downlink OFDM signals;wherein at least two of the second plurality of downlink signals have different downlink carrier frequencies and at least two of the second plurality of downlink signals have different downlink beams.

7. The method of claim 6 wherein each assignment information indicates the downlink carrier frequency of a respective one of the second plurality of OFDM signals.

8. The method of claim 6 wherein each downlink carrier frequency comprises a mutually non-overlapping band of sub-carriers.

9. The method of claim 6 further comprising transmitting, by the wireless user terminal, a plurality of uplink OFDM signals using at least two different uplink beams.

10. The method of claim 6 further comprising transmitting, by the wireless user terminal, a plurality of uplink OFDM signals using at least two different uplink carriers based on received uplink channel assignment information.

11. A wireless infrastructure device comprising: a plurality of antennas and a transmitter configured to transmit a first plurality of downlink orthogonal frequency division multiplexing (OFDM) signals on at least one downlink carrier frequency, wherein each of the first plurality of downlink OFDM signals includes assignment information for a wireless user terminal; andthe plurality of antennas and a receiver are configured to transmit a second plurality of downlink OFDM signals to the wireless user terminal, wherein each of the second plurality of downlink OFDM signals corresponds to the assignment information in a respective one of the first plurality of downlink OFDM signals;wherein a downlink carrier frequency and a downlink beam dynamically change over the second plurality of downlink OFDM signals; wherein at least two of the second plurality of downlink signals have different downlink carrier frequencies and at least two of the second plurality of downlink signals have different downlink beams.

12. The wireless infrastructure device of claim 11 wherein each assignment information indicates the downlink carrier frequency of a respective one of the second plurality of OFDM signals.

13. The wireless infrastructure device of claim 11 wherein each downlink carrier frequency comprises a mutually non-overlapping band of sub-carriers.

14. The wireless infrastructure device of claim 11 further comprising a receiver, wherein the plurality of antennas and the receiver is configured to receive a plurality of uplink OFDM signals from the wireless user terminal using at least two different uplink beams.

15. The wireless infrastructure device of claim 11 further comprising a receiver, wherein the plurality of antennas and the receiver is configured to receive a plurality of uplink OFDM signals from the wireless user terminal using at least two different uplink carriers based on received uplink channel assignment information.