TECHNICAL FIELD

The present invention relates generally to wireless communications systems, and more specifically, but not exclusively, to spectrum management techniques for point to multipoint wireless broadband communications systems that provide for increased data throughput and link availability through more efficient use of the electromagnetic spectrum allocated to the system.

BACKGROUND

In recent years, there has been an increasing need for wireless communications systems capable of carrying broadband data, and in particular for point-to-multipoint wireless systems in which a master wireless station is in communication with several slave wireless stations. For example, a point-to-multipoint system may provide backhaul systems and microwave Ethernet bridges, for example providing connectivity to small cell and macro cell infrastructure. Such a need has arisen for a variety of reasons, including the difficulties that users often experience in obtaining high speed Internet access service in some remote areas, and the convenience that wireless systems generally afford to users wishing to set up communications links and networks accessible from locations within urban environments or from locations dispersed across significant geographical distances. A conventional wireless broadband communications system can be set up as a line-of-sight (LOS) system or a non-line-of-sight (NLOS) system. The conventional LOS system typically includes a directional antenna deployed at one or more user locations within the line-of-sight of an antenna at a base station. The conventional NLOS system is typically configured as a multiple input multiple output (MIMO) system including a first plurality of antennas deployed at one end of a communications link, and a second plurality of antennas deployed at the other end of the communications link. Both the LOS system and the NLOS system may be employed in point-to-multipoint applications, in which a transmitter transmits signals over multiple communications channels using known space-time coding and modulation techniques, and one or more receivers capture the transmitted signals and employ signal processing techniques to decode and demodulate the signals to recover user data.

One problem facing conventional wireless broadband communications systems, whether they are configured as LOS or NLOS systems, is that the bandwidth capacity of the communications channels available to the systems is often limited, resulting in severe constraints in the communications capacity of the overall system. In a wireless communications system, such channels are typically defined within a limited portion of the electromagnetic spectrum allocated to the system. To achieve more efficient use of the allocated spectrum, wireless communications systems have employed digital communications techniques that allow data packets corresponding to separate communications sessions to be transmitted along multiple shared channels, obviating the need for a single dedicated channel for each communications session. Such techniques are frequently employed in wireless communications networks including one or more wireless LANs (WLANs), which utilize data packet protocols to communicate between the various nodes of the WLAN. The operational parameters for such WLANs are described in the IEEE 802.11 standard.

More recently, the use of shared frequency bands has exacerbated the problems relating to the constraints in the communications capacity of wireless broadband communications systems. Such a shared frequency band for WLANs is the unlicensed frequency band located at 5 GHz. Due to the unlicensed nature of the shared 5 GHz band, more than one WLAN operating in the 5 GHz band may be deployed within the same geographical area. Further, other types of wireless communications systems and radar operating in the 5 GHz band, or generating frequency harmonics having components in the 5 GHz band, may also be deployed within the same geographical area. As a result, the levels of noise and interference on the channels available to wireless communications systems are likely to increase, thereby significantly reducing data throughput and link availability. It is known to dynamically allocate spectrum in a point-to-point wireless communication system.

It would be desirable to have a point-to-multipoint wireless broadband communications system that makes more efficient use of the electromagnetic spectrum allocated to the system, and that avoids the limitations of prior art systems.

SUMMARY

In accordance with a first aspect of the invention there is provided a method of spectrum management in a point to multipoint wireless communications system comprising a master station and a plurality of slave stations operating according to a time division multiplex protocol, the wireless communications system being operable to transmit and receive signals using a plurality of frequency channels,

comprising the steps of:

periodically measuring, within a predetermined timeslot of the time division multiplex protocol in which the master station and the slave stations do not transmit, a noise and interference level associated with each one of the plurality of frequency channels at each of the plurality of slave stations;

generating a plurality of histograms of the noise and interference level measurements for each of the plurality of slave stations, each histogram being associated with a respective frequency channel, and each histogram comprising a plurality of bins, each bin corresponding to a predetermined range of noise and interference levels associated with the respective frequency channel;

determining a noise and interference level estimate for each frequency channel for each of the plurality of slave stations as a predetermined percentile of the histogram of measured noise and interference levels associated with the respective frequency channel for the respective slave station;

generating a respective single combined noise and interference level estimate for each frequency channel from at least the respective noise and interference level estimates for each of the plurality of slave stations; and

selecting one of the plurality of frequency channels for use in subsequent transmission of frames of the time division multiplex protocol on the basis of the respective single combined noise and interference level estimates.

This allows a common frequency channel to be selected for reception at each of the slave stations, taking into account the noise and interference environment at each of the slave stations, which may different at each slave station.

In an embodiment of the invention, the method comprises periodically sending noise and interference measurement data from each of the plurality of slave stations to the master station.

This allows the master station to determine combined noise and interference level estimates based on the measured data.

In an embodiment of the invention, the noise and interference measurement data sent from each of the plurality of slave stations to the master station comprises the determined noise and interference level estimate for each frequency channel, and the plurality of histograms is generated at the master station.

This allows the master station to carry out the processing intensive tasks and reduces the processing load on the slave stations, and allows the histograms at the master station to be updated continually.

In an embodiment of the invention, the noise and interference measurement data sent from each of the plurality of slave stations to the master station comprises a histogram of the noise and interference level measurements for the respective slave station for each frequency channel.

This allows signalling data to be reduced by sending processed data rather than raw data to the master station.

In an embodiment of the invention, determining a respective single combined noise and interference level estimate for each frequency channel comprises determining, for each frequency channel, a respective highest noise and interference level estimate of the noise and interference level estimates of each of the slave stations; and

selecting one of the plurality of frequency channels comprises selecting the frequency channel having the lowest of the respective highest noise and interference level estimates.

This allows a frequency channel to be selected which maintains good performance for the slave station suffering the worst interference.

In an embodiment of the invention, determining a respective single combined noise and interference level estimate for each frequency channel comprises determining, for each frequency channel, a respective mean noise and interference level estimate of the noise and interference level estimates of each of the slave stations; and

selecting one of the plurality of frequency channels comprises selecting the frequency channel having the lowest mean noise and interference level estimates.

This allows a frequency channel to be selected which maintains good throughput on average across the slave stations.

In an embodiment of the invention, the time division multiplex protocol is part of a time division duplex and time division multiplex protocol, and the selected frequency channel is for use in downlink timeslots of frames of the time division duplex and time division multiplex protocol.

Downlink timeslots are for use in transmission from the master to the slave stations.

In an embodiment of the invention, the selected frequency channel is for use in both uplink and downlink timeslots of frames of the time division duplex and time division multiplex protocol, the method comprising:

periodically measuring, within the predetermined timeslot of the time division duplex and time division multiplex protocol in which the master station and the slave stations do not transmit, a noise and interference level associated with each one of the plurality of frequency channels at the master station;

generating a plurality of histograms of the noise and interference level measurements for the master station; and

determining a noise and interference level estimate for each frequency channel for the master station as a predetermined percentile of the histogram of measured noise and interference levels associated with the respective frequency channel,

wherein the respective single combined noise and interference level estimate for each frequency channel is generated from the respective noise and interference level estimate for each of the plurality of slave stations and for the master station.

This allows a common frequency channel to be selected for reception at each of the slave stations and at the master station, taking into account the noise and interference environment at each of the slave stations and at the master station, which may different at each station.

In an embodiment of the invention, determining the respective single combined noise and interference level estimate for each frequency channel comprises determining, for each frequency channel, a respective highest noise and interference level estimate of the noise and interference level estimates for the master station and for each of the slave stations; and

selecting one of the plurality of frequency channels comprises selecting the frequency channel having the lowest of the respective highest noise and interference level estimates.

This allows a frequency channel to be selected which maintains good performance for the station suffering the worst interference.

In an embodiment of the invention, determining the respective single combined noise and interference level estimate for each frequency channel comprises determining, for each frequency channel, a respective mean noise and interference level estimate of the noise and interference level estimates of each of the slave stations and for the master station; and

selecting one of the plurality of frequency channels comprises selecting the frequency channel having the lowest mean noise and interference level estimates.

This allows a frequency channel to be selected which maintains good throughput on average across the slave stations and for the uplink and the downlink.

In an embodiment of the invention, the selected frequency channel is for use in downlink timeslots of frames of the time division duplex and time division multiplex protocol, and wherein the uplink timeslots of frames of the time division duplex and time division multiplex protocol use a second selected frequency.

In an embodiment of the invention, the method comprises periodically measuring, within the predetermined timeslot of the time division duplex and time division multiplex protocol in which the master station and the slave stations do not transmit, a noise and interference level associated with each one of the plurality of frequency channels at the master station;

generating a plurality of histograms of the noise and interference level measurements for the master station; and

determining a noise and interference level estimate for each frequency channel for the master station as a predetermined percentile of the histogram of measured noise and interference levels associated with the respective frequency channel; and

selecting a second of the plurality of frequency channels for use in subsequent uplink frames of the time division multiplex and time division multiplex protocol on the basis of the determined a noise and interference level estimate for each frequency channel for the master station.

This allows the downlink and the uplink to use different frequencies to allow improved throughput when, for example, the master station suffers interference at different frequencies than the slave stations.

In an embodiment of the invention, the method comprises:

sending a respective message from the master station to each slave station indicating the selected frequency channel; and

dependent on receipt of an acknowledgment from each slave station, sending a trigger signal to each slave station indicating that the selected frequency channel should be used for a subsequent frame of the time division multiplex protocol.

This allows an efficient transition to the use of a selected frequency.

In accordance with a second aspect of the invention, there is provided a point to multipoint wireless communications system comprising a master station and a plurality of slave stations operating according to a time division multiplex protocol, the wireless communications system being operable to transmit and receive signals using a plurality of frequency channels, wherein:

each slave station comprises a processor configured to cause the respective slave station to periodically measure, within a predetermined timeslot of the time division multiplex protocol in which the master station and the slave stations do not transmit, a noise and interference level associated with each one of the plurality of frequency channels at the respective slave station; and

the master station comprises a processor configured to cause the master wireless station to:

periodically receive noise and interference measurement data from each of the plurality of slave stations, the noise and interference measurement data having been measured, within a predetermined timeslot of the time division multiplex protocol in which the master station and the slave stations do not transmit;

generate a respective single combined noise and interference level estimate for each frequency channel from at least a respective noise and interference level estimate for each of the plurality of slave stations; and

select one of the plurality of frequency channels for use in subsequent transmission of frames of the time division multiplex protocol on the basis of the generated combined noise and interference level estimates,

wherein the respective single combined noise and interference level estimate for each frequency channel is generated from a plurality of histograms of the noise and interference level measurements for each of the plurality of slave stations, each histogram being associated with a respective frequency channel, and each histogram comprising a plurality of bins, each bin corresponding to a predetermined range of noise and interference levels associated with the respective frequency channel, by determining a noise and interference level estimate for each frequency channel for each of the plurality of slave stations as a predetermined percentile of the histogram of measured noise and interference levels associated with the respective frequency channel.

In accordance with a third aspect of the invention there is provided a master station of a point to multipoint wireless communications system comprising the master station and a plurality of slave stations, the wireless network being configured to operate according to a time division multiplex protocol and being operable to transmit and receive signals using a plurality of frequency channels, the master station comprising a processor configured to cause the master station to:

periodically receive noise and interference measurement data from each of the plurality of slave stations, the noise and interference measurement data having been measured, within a predetermined timeslot of the time division multiplex protocol in which the master station and the slave stations do not transmit;

generate a respective single combined noise and interference level estimate for each frequency channel from at least a respective noise and interference level estimate for each of the plurality of slave stations; and

select one of the plurality of frequency channels for use in subsequent transmission of frames of the time division multiplex protocol on the basis of the generated combined noise and interference level estimates,

wherein the respective single combined noise and interference level estimate for each frequency channel is generated from a plurality of histograms of the noise and interference level measurements for each of the plurality of slave stations, each histogram being associated with a respective frequency channel, and each histogram comprising a plurality of bins, each bin corresponding to a predetermined range of noise and interference levels associated with the respective frequency channel, by determining a noise and interference level estimate for each frequency channel for each of the plurality of slave stations as a predetermined percentile of the histogram of measured noise and interference levels associated with the respective frequency channel.

In accordance with a fourth aspect of the invention, there is provided a slave station of a point to multipoint wireless communications system comprising a master station and a plurality of slave stations operating according to a time division multiplex protocol, the wireless communications system being operable to transmit and receive signals using a plurality of frequency channels, the slave station comprising a processor configured to cause the slave station to:

periodically measure, within a predetermined timeslot of the time division multiplex protocol in which the master station and the slave stations do not transmit, a noise and interference level associated with each one of the plurality of frequency channels at the slave station; and

periodically transmit noise and interference measurement data to the master station, the noise and interference measurement data comprising at least one histograms of the noise and interference level measurements for the slave station, the histogram being associated with a respective frequency channel, and the histogram comprising a plurality of bins, each bin corresponding to a predetermined range of noise and interference levels associated with the respective frequency channel.

Further features of the invention will be apparent from the following description of preferred embodiments of the invention, which are given by way of example only.

