Guard interval adaptation for coordinated beamforming

A method of receiving an Orthogonal Frequency Division Multiplex, OFDM, symbol comprising a guard interval including a cyclically repeated part of an original symbol, the method comprising:

• receiving a signal comprising the OFDM symbol;
• determining from the signal whether only a first part of the guard interval or also a second part of the guard interval is used for the OFDM symbol, where the second part includes a repeated part in addition to the first part;
• assigning a transform window for the OFDM symbol based on the guard interval;
• and
• demodulating the OFDM symbol including performing a transform of information within the transform window;
• the second part of the guard interval comprising one of:
• an extended cyclic prefix in addition to the first part of the guard interval;
• and
• cyclic prefix;
• and
• the assigning of the transform window includes one of:
• overlapping the transform window with the second part of the cyclic prefix such that a final part of the OFDM symbol is outside the transform window;
• and
• overlapping the cyclic prefix part of the OFDM symbol with the transform window such that a final part of the OFDM symbol is outside the transform window.

A transmitter for transmitting an Orthogonal Frequency Division Multiplex, OFDM, symbol via a channel, the OFDM symbol comprising a guard interval including a cyclically repeated part of an original symbol OFDM symbol, the transmitter comprising:

• a transformer configured to transform a series of frequency domain data symbols into a burst of time domain symbols forming the original OFDM symbol;
• a symbol former configured to append to the time domain burst a first part of the guard interval for the OFDM symbol by duplication of a segment of the time domain burst, include an indication whether the guard interval further comprises a second part which is an extended guard interval part in relation to the first part of the guard interval, where the second part includes a repeated part in addition to the first part, and append the second part, when indicated, to the time domain burst;
• and
• transmitter circuitry configured to transmit the formed OFDM symbol.

A receiver for receiving an Orthogonal Frequency Division Multiplex, OFDM, symbol via a channel, the OFDM symbol comprising a guard interval including a cyclically repeated part of an original symbol OFDM symbol, the receiver comprising:

• receiver circuitry configured to receive a signal comprising the OFDM symbol;
• and
• demodulation circuitry configured to:
• determine from the signal whether only a first part of the guard interval or also a second part of the guard interval is used for the OFDM symbol, where the second part includes a repeated part in addition to the first part, assign a transform window for the OFDM symbol based on the guard interval, and;
• assign a transform window for the OFDM symbol based on the guard interval;
• demodulate the OFDM symbol including performing a transform of information within the transform window;
• the second part of the guard interval comprises one of:
• an extended cyclic prefix in addition to the first part of the guard interval;
• and
• cyclic prefix;
• and
• the assigning of the transform window includes one of:
• overlapping the transform window with the second part of the cyclic prefix such that a final part of the OFDM symbol is outside the transform window;
• and
• overlapping the cyclic prefix part of the OFDM symbol with the transform window such that a final part of the OFDM symbol is outside the transform window.

A non-transitory computer storage medium storing a computer program comprising instructions which, when executed on a processor of a transmitter, causes the transmitter to perform a method of transmitting an Orthogonal Frequency Division Multiplexing, OFDM, symbol comprising a guard interval including a cyclically repeated part of an original symbol, the method comprising

• applying a guard interval for the OFDM symbol, the guard interval comprising a first part, where the first part is a cyclic prefix;
• determining whether to use the second part of the guard interval, and when determined that the second part of the guard interval is to be used:
• including an indication that the applied guard interval comprises a second part, the second part being at least one of a cyclic prefix and a postfix;
• applying the second part of the guard interval;
• and
• transmitting the OFDM symbol;
• the determining whether to use the second part of the guard interval comprises:
• determining whether coordinated beamforming transmission is performed between neighbouring access points;
• estimating impact of transients emanating from changes in the coordinated beamforming;
• and
• determining to apply the second part of the guard interval when estimated impact of transients has a timing within the second part of the guard interval.