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US 6,628,707 B2Granted
Adaptive equalizer system for short burst modems and link hopping radio networks
AssigneeRadiant Networks PLC
InventorsManouchehr S. Rafie, Jun Lu, Dengwei Fu, Tushar Shah
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Abstract
A method for an adaptive equalization apparatus in a multiple-link hopping radio system includes hopping among a plurality of radio links to receive variable-length bursts of radio signals on the plurality of radio links and equalizing amplitude and phase variations of a slow channel for each radio link from a received burst on the radio link. Further, the method includes storing the estimated tap coefficients pertinent to each radio link and using the tap weights of the current burst of the radio link to reliably pre-compensate the channel amplitude and phase distortion of a next received burst on the radio link.
Claims26
A method for receiving and decoding burst radio signals from multiple sources, the method comprising:
- receiving bursts of radio signals on a plurality of radio links in a radio system;
- compensating amplitude and delay distortions for each radio link from a received burst on the plurality of radio links using a non-adaptive equalizer, a first adaptive equalizer I, a second adaptive equalizer II, the equalizers being K/M fractionally-spaced, K and M being integers and K≦M;
- pre-equalizing a received burst of a radio link using the non-adaptive equalizer, wherein tap coefficients of the non-adaptive equalizer are obtained from the adaptive equalizer II operated on a previous received burst of the radio link;
- estimating and removing carrier phase offset for the received burst;
- estimating initial tap coefficient values of the adaptive equalizer II using the first adaptive equalizer I operating on the current burst of a present radio link;
- adaptively equalizing a delayed version of the current burst using the adaptive equalizer II with the estimated tap coefficient values;
- storing the estimated tap coefficient values of the adaptive equalizer II into a memory unit at the end of the current burst of the operating radio link;
- and
- retrieving stored tap coefficients of an adaptive equalizer II from the memory unit into the non-adaptive equalizer to pre-compensate any residual amplitude and delay distortion of a next received burst on each radio link.
6 more elements
A method for receiving radio signals in a link-hopping, burst mode radio receiver, the method comprising:
- receiving a first burst of a first radio signal on a first radio link;
- determining equalizer weights for a first adaptive equalizer I about the first radio link using the first burst;
- subsequently, receiving a next burst of the first radio signal on the first radio link using the equalizer weights obtained in the first burst as initial tap coefficient values;
- storing equalizer weights of a second adaptive equalizer II at the end of the current burst to be used in a fixed equalizer to pre-compensate for amplitude and phase variations of received signals;
- receiving a first burst of a second radio signal on a second radio link;
- and
- determining equalizer weights for the second radio link using equalizer weights obtained in the first burst of the second radio signal as initial tap coefficient values of the first burst of the second radio signal;
- wherein receiving the first burst of the second radio signal comprises:
- determining channel information for the second radio link and storing equalizer weights for the second radio link for subsequent use;
- and
- using the stored information as initial equalizer weights of the first equalizer for a second burst of the second radio signal.
8 more elements
A method for receiving radio signals in a link-hopping, burst mode radio receiver, the method comprising:
- receiving a first burst of a first radio signal on a first radio link;
- determining equalizer weights for a first adaptive equalizer I about the first radio link using the first burst;
- subsequently, receiving a next burst of the first radio signal on the first radio link using the equalizer weights obtained in the first burst as initial tap coefficient values;
- and
- storing in a memory circuit coupled to the second adaptive equalizer II next burst equalizer weights for the fixed equalizer and the adaptive equalizer I on a present radio link;
- wherein determining the equalizer weights comprises downloading to a fixed equalizer complex coefficients from a second adaptive equalizer II for the first radio signal.
3 more elements
An adaptive, fractionally-spaced equalizer method for use in a multiple-link hopping, burst adaptive modem, the method comprising:
- receiving an amplitude and phase distorted complex signal as a series of bursts, each burst including one or more pilot symbols and data symbols;
- pre-compensating for amplitude and phase variations of the received complex signal using a fixed, fractionally-spaced equalizer;
- forming an estimation of carrier phase using a coarse estimation of carrier phase to estimate carrier phase for a burst using pilot and data symbols of the burst;
- estimating initial tap values of the second adaptive equalizer using a first adaptive equalizer I after an integer number of symbols;
- and
- equalizing the delayed version of the input received signal of the first adaptive equalizer in a second adaptive equalizer II.
3 more elements
An adaptive equalizer system for use in a link hopping burst adaptive modem in steady state operation, the system comprising:
- a random access digital memory with a plurality of storage locations that are predefined for multiple radio links and storing the tap coefficient values for the respective radio links;
- a fixed equalizer for pre-compensating amplitude and phase variations of a present data burst of a present link through the fixed equalizer for which the tap coefficient values pertinent to a previous burst of the present link are loaded from the memory, the fixed equalizer producing a pre-compensated amplitude and phase signal;
- a carrier phase recovery unit extracting distorted carrier phase for a plurality of communication links, the carrier phase unit including:
- a first stage which acquires a coarse estimate of the distorted carrier phase through a pilot-aided technique using multiple known pilot symbols contained in the present burst of data;
- a fixed phase bias removal stage coupled to the first stage;
- a complex conjugate phasor generating stage coupled to the fixed phase bias removal stage;
- a de-rotating means for de-rotating the equalized signal by a phasor signal generated by the phasor generating stage to remove estimated coarse carrier phase from the equalized signal to produce a coarse phase compensated signal;
- a data-aided phase estimator stage for removing modulated signal from the coarse phase compensated signal using a data-aided, decision-directed technique;
- an averaging means for averaging M symbols from the data-aided phase estimator stage to reduce noise variance;
- a first adaptive equalizer I unit for generating initial tap coefficient values for a second adaptive equalizer II which produces an equalized signal and stores tap coefficient values of the second adaptive equalizer II at the end of the current burst in the memory to be used as the tap coefficient values of a fixed equalizer for the next burst of a respective radio link.
7 more elements
Dependencies are inferred from the claim text.