Interference mitigation in a wireless communication system

• US 6,990,059 B1
• Filed: 09/05/2001
• Issued: 01/24/2006
• Est. Priority Date: 09/05/2001
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Botterill, Iain, Anikhindi, Santosh
• Primary Examiner(s): HO, DUC CHI
• Application Number:
  US09/947,283
• Time in Patent Office: 1,602 Days
• Field of Search: 370/208, 370/210, 370/330, 370/347, 370/252, 375/219, 375/346
• US Class Current: 370/208
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

By virtue of one embodiment of the present invention, dynamic signal to noise ratio measurements made on received signals are used to identify degraded segments of a channel. The degraded segments are then no longer used for transmitting payload data. In the context of an orthogonal frequency division multiplexing (OFDM) communication system, degraded OFDM subchannels, as determined on a real-time basis, are not used to transmit payload data. In an OFDM network where access is shared in the time domain among multiple transmitters and a single allocable time slot includes an integer number of OFDM bursts, the medium access control layer adjusts packet length, and therefore the amount of data to be included in a given slot, in response to the fluctuating number of available subchannels.

Claims

1. In a point to multipoint OFDM communication network, a method for operating a central access point, said method comprising:

monitoring reception quality in a plurality of OFDM subchannels;

designating a selected subchannel as below a quality threshold; and

instructing a subscriber unit to not transmit payload data in said selected subchannel,

wherein monitoring comprises;

receiving a series of OFDM bursts from said subscriber unit; and

measuring signal to noise ratio in said plurality of subchannels for each of said series of OFDM bursts, and

wherein receiving comprises;

receiving said series of OFDM bursts via a plurality of antennas;

statistically characterizing noise and/or interference superimposed on data symbols of said OFDM bursts based on predefined training symbols within said OFDM bursts; and

determining reception quality based on ratio of noise and/or interference to signal for said data symbols.

2. In a point to multipoint OFDM communication network, a method for operating a subscriber unit, said method comprising:

receiving an instruction message from a central access point, said instruction message including information identifying OFDM subchannels to be left unused in future upstream transmissions;

encoding data to be transmitted into an encoded packet in a manner that takes into account that there are OFDM subchannels left unused in accordance with said instruction message, and such that the encoded packet has a length that takes into account that there are OFDM subschannels left unused in transmission in accordance with said instruction message; and

transmitting said encoded data packet as one or more OFDM burst wherein OFDM subchannels are left unused in accordance with said instruction message.

3. In a point to multipoint OFDM communication network, apparatus for operating a central access point, said apparatus comprising:

an OFDM receiver that monitors reception quality in a plurality of OFDM subchannels; and

a control processor that designates a selected subchannel as below a quality threshold and instructs a subscriber unit to not transmit payload data in said selected subchannel,

wherein said OFDM receiver comprises;

a plurality of converters that convert time domain OFDM bursts received from said subscriber unit via a plurality of antennas into frequency domain OFDM bursts; and

an antenna combining block that statistically characterizes noise and/or interference superimposed on data symbols of said frequency domain OFDM bursts based on predefined training symbols within said frequency domain OFDM bursts; and

wherein reception quality is determined based on ratio of noise and/or interference to signal for said data symbols.

4. In a point to multipoint OFDM communication network, apparatus for operating a subscriber unit, said apparatus comprising:

a control processor configured to receive an instruction message from a central access point, said instruction message including information identifying OFDM subchannels to be left unused in future upstream transmissions;

an error correction encoder configured to encode data to be transmitted into an encoded packet in a manner that takes into account that there are OFDM subschannels left unused in accordance with said instruction message, and such that the encoded packet has a length that takes into account that there are OFDM subchannels are left unused in transmission in accordance with said instruction message; and

an OFDM transmitter configured to transmit said encoded packet as one or more OFDM bursts wherein OFDM subschannels are left unused in accordance with said instruction message.