PATENT DOCUMENT

Publication Number: US-10476719-B2
Application Number: US-201916433273-A
Country: US
Kind Code: B2

Title: Pilot symbol patterns for transmission through a plurality of antennas

Abstract:
A method and apparatus for improving channel estimation within an OFDM communication system. Channel estimation in OFDM is usually performed with the aid of pilot symbols. The pilot symbols are typically spaced in time and frequency. The set of frequencies and times at which pilot symbols are inserted is referred to as a pilot pattern. In some cases, the pilot pattern is a diagonal-shaped lattice, either regular or irregular. The method first interpolates in the direction of larger coherence (time or frequency). Using these measurements, the density of pilot symbols in the direction of faster change will be increased thereby improving channel estimation without increasing overhead. As such, the results of the first interpolating step can then be used to assist the interpolation in the dimension of smaller coherence (time or frequency).

Claims:
What is claimed is: 
     
       1. An apparatus comprising:
 a processor, wherein the processor is configured to receive transmissions via one or more receive antennas, wherein the processor is configured to:
 receive, via the one or more receive antennas, a signal including four antenna scattered pilot symbol patterns in a plurality of time intervals and a plurality of subcarriers in frequency, wherein each time interval of the plurality of time intervals spans seven orthogonal frequency division multiplexing (OFDM) symbol durations in time, wherein a first and second antenna scattered pilot symbol pattern of the four antenna scattered pilot symbol patterns are identical versions of each other shifted in frequency, wherein a third and fourth antenna scattered pilot symbol pattern of the four antenna scattered pilot symbol patterns are identical patterns shifted in frequency, wherein the first and third antenna scattered pilot symbol patterns are not shifted versions of each other, wherein the four antenna scattered pilot symbol patterns are mapped to pilot symbol positions on exactly three of the seven OFDM symbols of each time interval of the plurality of time intervals, and wherein a repetition of each of the four antenna scattered pilot symbol patterns are received in each interval of the plurality of time intervals. 
 
 
     
     
       2. The apparatus of  claim 1 ,
 wherein to receive the four antenna scattered pilot symbol patterns from a transmitter, the processor is further configured to:
 receive pilot symbol positions of exactly a first two of the four antenna scattered pilot symbol patterns in a first of the exactly three of the seven OFDM symbols of each time interval of the plurality of time intervals; and 
 receive pilot symbol positions of exactly a second two of the four antenna scattered pilot symbol patterns in a second of the exactly three of the seven OFDM symbols of each time interval of the plurality of time intervals, wherein the first two antenna scattered pilot symbol patterns and second two antenna scattered pilot symbol patterns are disjoint. 
 
 
     
     
       3. The apparatus of  claim 1 ,
 wherein the four antenna scattered pilot symbol patterns are disjoint, and 
 wherein the pilot symbol positions of the four antenna scattered pilot symbol patterns in each time interval of the plurality of time intervals collectively include:
 a first set of two pilot symbol positions at a first subcarrier and in first consecutive OFDM symbols; 
 a second set of two pilot symbol positions in a second OFDM symbol, wherein one pilot symbol position of the second set of two pilot symbol positions is on the first subcarrier, wherein the first consecutive OFDM symbols and the second OFDM symbol are non-consecutive with each other in time. 
 
 
     
     
       4. The apparatus of  claim 3 ,
 wherein the first set of two pilot symbol positions and the second set of two pilot symbol positions recur in their respective OFDM symbols at subcarriers with a common frequency spacing. 
 
     
     
       5. The apparatus of  claim 3 , wherein the pilot symbol positions of the four antenna scattered pilot symbol patterns in each time interval of the plurality of time intervals further collectively include:
 a third set of two pilot symbol positions at a second subcarrier and in the first consecutive OFDM symbols, 
 wherein each of the two pilot symbol positions of the first set correspond to a respective one of the first and second antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns, 
 wherein each of the two pilot symbol positions of the third set correspond to a respective one of the third and fourth antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns, and 
 wherein the second subcarrier is non-adjacent to the first subcarrier in frequency. 
 
     
     
       6. The apparatus of  claim 5 ,
 wherein the one pilot symbol position of the second set of two pilot symbol positions on the first subcarrier corresponds to the third antenna scattered pilot symbol pattern of the four antenna scattered pilot symbol patterns. 
 
     
     
       7. The apparatus of  claim 5 , wherein the pilot symbol positions of the four antenna scattered pilot symbol patterns in each time interval of the plurality of time intervals further collectively include:
 a fourth set of two pilot symbol positions in the second OFDM symbol, 
 wherein one pilot symbol position of the fourth set of two pilot symbol positions is on the second subcarrier, 
 wherein each of the two pilot symbol positions of the second set of two pilot symbol positions correspond to a respective one of the third and fourth antenna scattered pilot symbol patterns of the antenna scattered pilot symbol patterns, and 
 wherein each of the two pilot symbol positions of the fourth set of two pilot symbol positions correspond to a respective one of the first and second antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns. 
 
     
     
       8. A user equipment device (UE) comprising:
 one or more receive antennas; and 
 a processor, wherein the processor is configured to receive transmissions via the one or more receive antennas, wherein the UE is configured to:
 receive, via the one or more receive antennas, a signal including four antenna scattered pilot symbol patterns in a plurality of time intervals and a plurality of subcarriers in frequency, wherein each time interval of the plurality of time intervals spans seven orthogonal frequency division multiplexing (OFDM) symbol durations in time, wherein a first and second antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns are identical versions of each other shifted in frequency, wherein a third and fourth antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns are identical patterns shifted in frequency, wherein the first and third antenna scattered pilot symbol patterns are not shifted versions of each other, wherein the four antenna scattered pilot symbol patterns are mapped to pilot symbol positions on exactly three of the seven OFDM symbols of each time interval of the plurality of time intervals, and wherein a repetition of each of the four antenna scattered pilot symbol patterns are received in each interval of the plurality of time intervals. 
 
 
     
     
       9. The UE of  claim 8 , wherein to receive the four antenna scattered pilot symbol patterns from a transmitter, the processor is further configured to:
 receive pilot symbol positions of exactly a first two of the four antenna scattered pilot symbol patterns in a first of the exactly three of the seven OFDM symbols of each time interval of the plurality of time intervals; and 
 receive pilot symbol positions of exactly a second two of the four antenna scattered pilot symbol patterns in a second of the exactly three of the seven OFDM symbols of each time interval of the plurality of time intervals, wherein the first two antenna scattered pilot symbol patterns and second two antenna scattered pilot symbol patterns are disjoint. 
 
     
     
       10. The UE of  claim 8 ,
 wherein the four antenna scattered pilot symbol patterns are disjoint, and 
 wherein the pilot symbol positions of the four antenna scattered pilot symbol patterns in each time interval of the plurality of time intervals collectively include:
 a first set of two pilot symbol positions at a first subcarrier and in first consecutive OFDM symbols; 
 a second set of two pilot symbol positions in a second OFDM symbol, wherein one pilot symbol position of the second set of two pilot symbol positions is on the first subcarrier, wherein the first consecutive OFDM symbols and the second OFDM symbol are non-consecutive with each other in time. 
 
 
     
     
       11. The UE of  claim 10 ,
 wherein the first set of two pilot symbol positions and the second set of two pilot symbol positions recur in their respective OFDM symbols at subcarriers with a common frequency spacing. 
 
     
     
       12. The UE of  claim 10 , wherein the pilot symbol positions of the four antenna scattered pilot symbol patterns in each time interval of the plurality of time intervals further collectively include:
 a third set of two pilot symbol positions at a second subcarrier and in the first consecutive OFDM symbols, 
 wherein each of the two pilot symbol positions of the first set correspond to a respective one of the first and second antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns, 
 wherein each of the two pilot symbol positions of the third set correspond to a respective one of the third and fourth antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns, and 
 wherein the second subcarrier is non-adjacent to the first subcarrier in frequency. 
 
     
     
       13. The UE of  claim 12 ,
 wherein the one pilot symbol position of the second set of two pilot symbol positions on the first subcarrier corresponds to the third antenna scattered pilot symbol pattern of the four antenna scattered pilot symbol patterns. 
 
     
     
       14. The UE of  claim 12 , wherein the pilot symbol positions of the four antenna scattered pilot symbol patterns in each time interval of the plurality of time intervals further collectively include:
 a fourth set of two pilot symbol positions in the second OFDM symbol, 
 wherein one pilot symbol position of the fourth set of two pilot symbol positions is on the second subcarrier, 
 wherein each of the two pilot symbol positions of the second set of two pilot symbol positions correspond to a respective one of the third and fourth antenna scattered pilot symbol patterns of the antenna scattered pilot symbol patterns, and 
 wherein each of the two pilot symbol positions of the fourth set of two pilot symbol positions correspond to a respective one of the first and second antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns. 
 
     
     
       15. A base station comprising:
 four transmit antennas; 
 digital circuitry, wherein the digital circuitry is configured to:
 transmit, via four transmit antennas, a signal including four antenna scattered pilot symbol patterns in a plurality of time intervals and a plurality of subcarriers in frequency, wherein each time interval of the plurality of time intervals spans seven orthogonal frequency division multiplexing (OFDM) symbol durations in time, wherein a first and second antenna scattered pilot symbol pattern of the four antenna scattered pilot symbol patterns are identical versions of each other shifted in frequency, wherein a third and fourth antenna scattered pilot symbol pattern of the four antenna scattered pilot symbol patterns are identical patterns shifted in frequency, wherein the first and third antenna scattered pilot symbol patterns are not shifted versions of each other, wherein the four antenna scattered pilot symbol patterns are mapped to pilot symbol positions on exactly three of the seven OFDM symbols of each time interval of the plurality of time intervals, and wherein a repetition of each of the four antenna scattered pilot symbol patterns are transmitted in each interval of the plurality of time intervals. 
 
 
     
     
       16. The base station of  claim 15 ,
 wherein to transmit the four antenna scattered pilot symbol patterns, the digital circuitry is further configured to:
 transmit pilot symbol positions of exactly a first two of the four antenna scattered pilot symbol patterns in a first of the exactly three of the seven OFDM symbols of each time interval of the plurality of time intervals; and 
 transmit pilot symbol positions of exactly a second two of the four antenna scattered pilot symbol patterns in a second of the exactly three of the seven OFDM symbols of each time interval of the plurality of time intervals, wherein the first two antenna scattered pilot symbol patterns and second two antenna scattered pilot symbol patterns are disjoint. 
 
 
     
     
       17. The base station of  claim 15 ,
 wherein the four antenna scattered pilot symbol patterns are disjoint, and 
 wherein the pilot symbol positions of the four antenna scattered pilot symbol patterns in each time interval of the plurality of time intervals collectively include:
 a first set of two pilot symbol positions at a first subcarrier and in first consecutive OFDM symbols; 
 a second set of two pilot symbol positions in a second OFDM symbol, wherein one pilot symbol position of the second set of two pilot symbol positions is on the first subcarrier, wherein the first consecutive OFDM symbols and the second OFDM symbol are non-consecutive with each other in time. 
 
 
     
     
       18. The base station of  claim 17 ,
 wherein the pilot symbol positions of the four antenna scattered pilot symbol patterns in each time interval of the plurality of time intervals further collectively include:
 a third set of two pilot symbol positions at a second subcarrier and in the first consecutive OFDM symbols, 
 wherein each of the two pilot symbol positions of the first set correspond to a respective one of the first and second antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns, 
 wherein each of the two pilot symbol positions of the third set correspond to a respective one of the third and fourth antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns, and 
 wherein the second subcarrier is non-adjacent to the first subcarrier in frequency. 
 
 
     
     
       19. The base station of  claim 18 ,
 wherein the one pilot symbol position of the second set of two pilot symbol positions on the first subcarrier corresponds to the third antenna scattered pilot symbol pattern of the four antenna scattered pilot symbol patterns. 
 
     
     
       20. The base station of  claim 18 , wherein the pilot symbol positions of the four antenna scattered pilot symbol patterns in each time interval of the plurality of time intervals further collectively include:
 a fourth set of two pilot symbol positions in the second OFDM symbol, 
 wherein one pilot symbol position of the fourth set of two pilot symbol positions is on the second subcarrier, 
 wherein each of the two pilot symbol positions of the second set of two pilot symbol positions correspond to a respective one of the third and fourth antenna scattered pilot symbol patterns of the antenna scattered pilot symbol patterns, and 
 wherein each of the two pilot symbol positions of the fourth set of two pilot symbol patterns correspond to a respective one of the first and second antenna scattered pilot symbol patterns of the four antenna scattered pilot symbol patterns.

Description:
PRIORITY CLAIM INFORMATION 
     This application is a continuation of U.S. patent application Ser. No. 16/255,702, filed on Jan. 23, 2019, titled “Pilot Symbol Patterns for Transmission through a Plurality of Antennas”, by Jianglei Ma et al., which is a continuation of 
     U.S. patent application Ser. No. 16/110,205, filed on Aug. 23, 2018, (issued as U.S. Pat. No. 10,200,226 on Feb. 5, 2019) titled “Pilot Symbol Patterns for Transmission through a Plurality of Antennas”, by Jianglei Ma et al., which is a continuation of 
     U.S. patent application Ser. No. 15/891,750, filed on Feb. 8, 2018, (issued as U.S. Pat. No. 10,075,314 on Sep. 11, 2018) titled “Pilot Symbol Patterns for Transmission via a Plurality of Antennas”, by Jianglei Ma et al., which is a continuation of 
     U.S. patent application Ser. No. 15/642,956, filed on Jul. 6, 2017, (issued as U.S. Pat. No. 9,929,889 on Mar. 27, 2018) titled “Pilot Symbol Patterns for Transmission via a Plurality of Antennas”, by Jianglei Ma et al., which is a continuation of 
     U.S. patent application Ser. No. 15/226,101, filed on Aug. 2, 2016, (issued as U.S. Pat. No. 9,705,720 on Jul. 11, 2017) titled “Pilot Symbol Patterns for Transmission via a Plurality of Antennas”, by Jianglei Ma et al., which is a continuation of 
     U.S. patent application Ser. No. 15/046,934, filed on Feb. 18, 2016, (issued as U.S. Pat. No. 9,432,232 on Aug. 30, 2016) titled “Pilot Symbol Patterns for Transmit Antennas”, by Jianglei Ma et al., which is a continuation of 
     U.S. patent application Ser. No. 13/944,022, filed on Jul. 17, 2013 (issued as U.S. Pat. No. 9,270,510 on Feb. 23, 2016), titled “Adaptive Two-Dimensional Channel Interpolation”, by Jianglei Ma et al., which is a continuation of 
     U.S. patent application Ser. No. 13/665,982, filed on Nov. 1, 2012 (issued as U.S. Pat. No. 8,842,756 on Sep. 23, 2014), titled “Adaptive Two-Dimensional Channel Interpolation”, which is a continuation of 
     U.S. patent application Ser. No. 12/064,566, filed on Sep. 4, 2008 (issued as U.S. Pat. No. 8,331,465 on Dec. 11, 2012), which is a U.S. National Stage of 
     International Application No. PCT/CA2006/001380, filed on Aug. 22, 2006, which claims the benefit of priority to: 
     U.S. Provisional Application No. 60/722,744, filed on Sep. 30, 2005; and 
     U.S. Provisional Application No. 60/710,527, filed on Aug. 23, 2005. 
     All of the above identified Applications are incorporated by reference in their entireties as though fully and completely set forth herein. 
     The claims in the instant application are different than those of the parent application or other related applications. The Applicant therefore rescinds any disclaimer of claim scope made in the parent application or any predecessor application in relation to the instant application. The Examiner is therefore advised that any such previous disclaimer and the cited references that it was made to avoid, may need to be revisited. Further, any disclaimer made in the instant application should not be read into or against the parent application or other related applications 
    
    
     BACKGROUND 
     Field of the Application 
     This invention relates to Orthogonal Frequency Division Multiplexing (OFDM) communication systems, and more particularly to channel interpolation with the use of pilot symbols. 
     Background of the Disclosure 
     In wireless communication systems that employ OFDM, a transmitter transmits data to a receiver using many sub-carriers in parallel. The frequencies of the sub-carriers are orthogonal. 
     Channel estimation in OFDM is usually performed with the aid of known pilot symbols which are sparsely inserted in a stream of data symbols. The attenuation of the pilot symbols is measured and the attenuations of the data symbols in between these pilot symbols are then estimated/interpolated. 
     Pilot symbols are overhead, and should be as few in number as possible in order to maximize the transmission rate of data symbols. It is desirable that channel estimation in OFDM be as accurate as possible without sacrificing bandwidth. 
     SUMMARY 
     In one embodiment, there is provided a method comprising receiving channel estimates for four pilot symbols in a scattered pilot pattern in time-frequency; calculating the channel response for the pilot symbols in both a first direction and a second direction; determining whether the channel changes more slowly in one direction than the other; and interpolating in the direction of slower channel change. 
     In some embodiments, the method of further comprises interpolating in the direction of faster channel change. 
     In some embodiments, the step of interpolating in the direction of faster channel change is performed using the result from the step of interpolating in the direction of slower channel change. 
     In some embodiments, the channel changes are calculated by performing an inner products operation. 
     In some embodiments, the first direction is a time direction and the second direction is a frequency direction. 
     In some embodiments, the first direction is a frequency direction and the second direction is a time direction. 
     In some embodiments, the scattered pilot pattern is a regular diamond lattice. 
     In some embodiments, the scattered pilot pattern is an irregular diamond lattice. 
     In some embodiments, the scattered pilot pattern is kite shaped. 
     In another embodiment, there is provided an OFDM receiver comprising: one or more receive antennas; the OFDM transmitter being adapted to receive channel estimates for four pilot symbols in a scattered pilot pattern in time-frequency, calculate channel changes for the pilot symbols in a first direction and a second direction, and interpolate in the direction of slower channel change. 
     In yet another embodiment, there is provided a method of interpolation using a set of four pilot symbols in a scattered pilot pattern in time-frequency wherein the set of four pilot symbols comprise first and second pilot symbols on a common sub-carrier frequency, spaced in time, and third and fourth pilot symbols transmitted on different sub-carriers on a common OFDM symbol period, the method comprising: determining a first channel change between the first and second pilot symbols; determining a second channel change between the third and fourth pilot symbols; determining which of the first and second channel change is slower; if the first channel change is slower, interpolating using the first and second pilot symbols to generate a channel estimate for the common sub-carrier frequency at the common OFDM symbol period, and then using the channel estimate in subsequent interpolations to determine other channel estimates; and if the second channel change is slower, interpolating using the third and fourth pilot symbols to generate a channel estimate for the common sub-carrier frequency at the common OFDM symbol period, and then using the channel estimate in subsequent interpolations to determine other channel estimates. 
     In yet another embodiment, a method of inserting pilot symbols into OFDM sub-frames for transmission by a plurality of transmitting antenna, the OFDM sub-frames having a time domain and a frequency domain, each OFDM sub-frame comprising a plurality of OFDM symbols, the method comprising: for each sub-frame, defining a set of at least two OFDM symbols none of which are consecutive that are to contain pilot symbols; at each antenna, inserting pilot symbols in each of the set of at least two OFDM symbols in a scattered pattern that does not interfere with the scattered pattern inserted by any other antenna. 
     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will now be described with reference to the attached drawings in which: 
         FIG. 1  is a diagram of a single antenna perfect diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 2  is a flowchart of a method of performing adaptive interpolation in accordance with one embodiment of the present invention; 
         FIG. 3  presents simulation results for one example of adaptive interpolation; 
         FIG. 4A  is a diagram of a single antenna irregular diamond lattice scattered pilot pattern which can used in accordance with an embodiment of the present invention; 
         FIG. 4B  is a diagram of a single antenna irregular diamond lattice scattered pilot pattern which can used in accordance with an embodiment of the present invention; 
         FIG. 5A  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 5B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 5C  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 5D  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 6  is a diagram of a single antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 7A  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 7B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 7C  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 7D  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 8  is a diagram of a single antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 9A  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 9B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 9C  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 9D  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 10A  is a diagram of a one antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 10B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 11A  is a diagram of a one antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 11B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 12A  is a diagram of a one antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 12B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention; 
         FIG. 13  is a block diagram of a cellular communication system; 
         FIG. 14  is a block diagram of an example base station that might be used to implement some embodiments of the present invention; 
         FIG. 15  is a block diagram of an example wireless terminal that might be used to implement some embodiments of the present invention; 
         FIG. 16  is a block diagram of a logical breakdown of an example OFDM transmitter architecture that might be used to implement some embodiments of the present invention; 
         FIG. 17  is a block diagram of a logical breakdown of an example OFDM receiver architecture that might be used to implement some embodiments of the present invention; and 
         FIG. 18  is a block diagram of one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Channel estimation in OFDM is usually performed with the aid of pilot symbols. More particularly, at an OFDM transmitter, known pilot symbols are periodically transmitted along with data symbols. The pilot symbols are typically spaced in time and frequency. 
     The variations in phase and amplitude resulting from propagation across an OFDM channel are referred to as the channel response. The channel response is usually frequency and time dependent. If an OFDM receiver can determine the channel response, the received signal can be corrected to compensate for the channel degradation. The determination of the channel response is called channel estimation. The transmission of known pilot symbols along with data symbols allows the receiver to carry out channel estimation. 
     When a receiver receives an OFDM signal, the receiver compares the received value of the pilot symbols with the known transmitted value of the pilot symbols to estimate the channel response. 
     Since the channel response can vary with time and with frequency, the pilot symbols are scattered amongst the data symbols to provide a range of channel responses over time and frequency. The set of frequencies and times at which pilot symbols are inserted is referred to as a pilot pattern. In some cases, the pilot pattern is a diagonal-shaped lattice, either regular or irregular. 
       FIG. 1  is an example pilot pattern which can be used in accordance with one embodiment of the present invention. Pilot and data symbols are spread over an OFDM sub-frame in a time direction  120  and a frequency direction  122 . Most symbols within the OFDM sub-frame are data symbols  124 . Pilot symbols  126  are inserted in a diamond lattice pattern. In the illustrated example, the diamond lattice pattern in which each encoded pilot symbols are inserted within the OFDM sub-frame is a perfect diamond lattice pattern as illustrated by pilot symbols h 1 , h 2 , h 3  and h 4 . 
     A two dimensional interpolator is used to estimate the channel response at point h which is between four points of known channel response, i.e. pilot symbols h 1 , h 2 , h 3  and h 4 . Point h can then be used as an additional point from which the receiver can carry out channel estimation. The use of point h would, of course, not add any overhead to the OFDM signal. 
     The channel interpolation scheme is adaptive, i.e. it is a scheme which can adapt to varying conditions in the
 
 h ( i,j )= w   1 ( i,j ) h   1   +w   2 ( i,j ) h   2   +w   3 ( i,j ) h   3   +w   4 ( i,j ) h   4  
 
channel. The following formula presents a particular example of adaptive two-dimensional (time direction and frequency direction) interpolator to calculate point h:
 
where  w   1 ( i,j )+ w   2 ( i,j )+ w   3 ( i,j )+ w   4 ( i,j )=1.
 
     In this case, the two dimensional channel interpolation can be viewed as the sum of two one-dimensional interpolations. 
     The weights w k (i,j) may be adapted to coherence time and frequency of the channel. In some embodiments, if the channel coherence is less in the time direction than it is in the frequency direction, then h would be calculated using the following formula:
 
 h ( i,j )= w   1 ( i,j ) h   1   +w   2 ( i,j ) h   2   +w   3 ( i,j ) h   3   +w   4 ( i,j ) h   4  
 
where
 
 w   3 ( i,j )=0,
 
 w   4 ( i,j )=0, and
 
 w   1 ( i,j )+ w   2 ( i,j )=1.
 
     Alternatively, if the channel coherence is greater in the time direction than it is in the frequency direction, then h would be calculated using the following formula:
 
 h ( i,j )= w   1 ( i,j ) h   1   +w   2 ( i,j ) h   2   +w   3 ( i,j ) h   3   +w   4 ( i,j ) h   4  
 
where
 
 w   1 ( i,j )=0,
 
 w   2 ( i,j )=0, and
 
 w   3 ( i,j )+ w   4 ( i,j )=1.
 
     In another embodiment, the weights in both directions (time and frequency) are adaptively changed according to the channel coherence in the time and frequency directions as follows:
 
 h ( i,j )= c   time   w   1 ( i,j ) h   1   +c   time   w   2 ( i,j ) h   2   +c   freq   w   3 ( i,j ) h   3   +c   freq   w   4 ( i,j ) h   4  
 
 c   time   +c   freq =1
 
 w   1 ( i,j )+ w   2 ( i,j )+ w   3 ( i,j ) w   4 ( i,j )=1
 
     According to one embodiment, the sequence of interpolation is adapted to the coherence of the channel. 
     One way to achieve adaptive interpolation is to divide the interpolation into two one-dimensional steps as shown in the flowchart illustrated in  FIG. 2 :
         i. at step  210 , calculate the channel changes in both time and frequency directions and determine in which direction the channel changes faster;   ii. at step  220 , perform one-dimensional interpolation in the direction with slower channel change to calculate h; and   iii. at step  230 , using h, perform one-dimensional interpolation in the direction with faster channel change.       

     The method of adaptive interpolation set out above takes advantage of the fact that interpolated results from the direction of larger coherence time/frequency is more reliable, and hence is interpolated first. The calculation of h will effectively increase the density of pilot symbols in the direction of faster change thereby improving channel estimation without increasing overhead. As such, the results of the first interpolating step can then be used to assist the interpolation in the dimension of smaller coherence time/frequency. 
     In general, there are at least three ways to evaluate the channel change between two pilots, including:
         i. Euclidean distance. One problem with Euclidean distance, however, is that it is not sensitive to phase change;   ii. Phase change. One problem with phase change, however, is computation complexity; and   iii. Amplitude change. One problem with amplitude change, however, is that it is insensitive to phase change.       

     In light of these drawbacks a way to measure channel change so as to take both amplitude change and phase change into account, while at the same time keeping the computation complexity to a minimum, is desirable. According to an embodiment of the invention, therefore, a way of using the inner products of the two pilot assisted channel estimates as a measurement of channel change is shown below.
 
Λ time   =     h   3   ,h   4     =|h   3   ∥h   4 |cos(θ 3,4 )
 
Λ freq   =     h   1   ,h   2     |h   1   ∥h   2 |cos(θ 1,2 )
 
     Λ time  denotes channel change in the time direction. 
     Λ freq  denotes channel change in the frequency direction. 
     The term “&lt;h n ·h m &gt;” denotes the inner product of h n  and h m . 
     The term “|h n |” denotes the magnitude of the vector h n . If h n =a+bi then |h n |=sqr(a 2 +b 2 ). 
     The term “cos(θ1,2)” denotes the cosine of the difference in angle between h n  and h m : cos(θn,m)=cos(θn−θm). If h n =a+bi then θn can be calculated as θn=tan −1 (b/a). 
     The vector h n  can be represented as h 1 =|h 1 |e iθn , or as h n =a+bi, where
 
α=| h   n |cos(θ n ), and  b=|h   n |sin(θ n ).
 
     When the amplitude changes linearly between the two channel estimates, the maximum Λ is achieved when |h 1 |=|h 2 | in frequency and |h 3 |=|h 4 | in time. 
     Hence the more the channel changes, the smaller the Λ, regardless whether this change is in amplitude or phase. The inner product is able to solve phase ambiguity. When |θ|&gt;π/2 (which rarely occurs), cos(θ) becomes negative, and hence smaller. An inner product may then be computed, which requires two real multiplications and one real addition, and the result is therefore a real number. 
     Referring again to  FIG. 1 , what follows is an example of the adaptive interpolation method. 
     Assume:
 
 h   1 =0.4423−1.0968 i  
 
 h   2 =−0.0051−0.1484 i  
 
 h   3 =0.1258−0.3413 i  
 
 h   4 =0.3958−0.5883 i  
 
     The central point, known from a simulation, has the value of h=0.2859−0.4224i. 
     The inner product is then calculated as follows:
 
   h   1   ·h   2   =0.1605
 
   h   3   ·h   4   =0.2506
 
where    h   1   ·h   2   =denotes the inner product of  h   1  and  h   2 .
 
     If h 1 =a 1 +ib 1  and h 2 =a 2 +ib 2  then the inner product can be calculated as
 
   h   1   ·h   2     =a   1   a   2   +b   1   b   2 .
 
     Alternatively,  h 1 ·h 2   =|h 1 ∥h 2 |cos(θ 2 −θ 1 ). 
     Since  h 1 ·h 2   &lt; h 3 ·h 4   , the channel changes faster in the h 1 /h 2  direction. 
     h is then estimated in both the frequency and time directions:
 
 {tilde over (h)}   h1,h2 =0.5( h   1   +h   2 )=0.2186−0.6226 i  
 
 {tilde over (h)}   h3,h4 =0.5( h   3   +h   4 )=0.2608−0.4648 i  
 
     Compared with the known h, obviously {tilde over (h)} h3,h4  provides a better estimate {tilde over (h)} h1,h2 ; hence {tilde over (h)} h3,h4  can be used to improve the channel interpolation quality in the h 1 /h 2  direction. 
     Note that there is no requirement that h be the middle point equidistant from h 1 , h 2 , h 3  and h 4 . 
     In the example above, the interpolation sequence was determined to be:
         i. interpolate between the two pilots in the time direction first to calculate h, and   ii. use h and/or one or both of the two pilots to interpolate in the frequency direction.       

     Of course, if the initial calculation used to determine which channel direction changes faster determines that the h 3 /h 4  direction changes faster, then the interpolation sequence will be:
         i. interpolate between the two pilots in the frequency direction first to calculate h, and   ii. use h and/or one or both of the two pilots to interpolate in the time direction.       

     Once h is calculated, any one of a number of conventional channel estimation techniques can be used. Such channel estimation techniques typically consist of two steps. First, the attenuations at the pilot positions are measured. This measurement is calculated using the formula: 
               H   ⁡     (     n   ,   k     )       ≡       Y   ⁡     (     n   ,   k     )         X   ⁡     (     n   ,   k     )               
where X(n,k) is the known pilot symbol, and Y(n,k) is the received pilot symbol.
 
     These measurements are then used to estimate (interpolate) the attenuations of the data symbols in the second step. Persons skilled in the art will appreciate that such channel estimation techniques include, but are not limited to, linear interpolation, second order interpolation, maximum likelihood (least square in time domain), linear minimum square error and others. 
     In another embodiment, a “majority vote” is used to determine the interpolation sequence for all the “diamonds” across the frequency domain. This means that there are several calculations performed along the frequency direction for the channel change. Some results will indicate there is more change in time, while other results indicate there is more change in frequency. The “majority vote” option means the choice whether to interpolate first in the time direction or the frequency direction is arrived at by assessing the majority of the results. For example, if the majority of the results indicate that the channel changes faster in the time direction, then interpolation is first performed in the frequency direction, and then in the time direction. If the majority of the results indicate that the channel changes faster in the frequency direction, then interpolation is first performed in the time direction, and is then performed in the frequency direction. 
     In accordance with an embodiment of the invention,  FIG. 3  presents simulation results for the adaptive interpolation method described above. The results show the benefit of adaptive interpolation when channel changes slower in the time direction when UE speed is low, and slower in the frequency direction when UE speed is high. The curve of “ideal channel” is of the case with clean known channel, i.e. with no interpolation loss and additive noise. As shown this approach recoups most of the interpolation loss. The results were obtained with the majority vote option described above. 
     It is not necessary that there be a regular diamond shaped pilot pattern in order to use the adaptive interpolation method described above. For example, an irregular diamond shaped pilot pattern can be used in accordance with other embodiments of the present invention, such as the scattered pilot patterns shown in  FIGS. 4A to 11 . In  FIGS. 4A to 11 , the number of OFDM symbols per Transmission Time Interval (TTI) is odd instead of even. In some embodiments, the scattered pilot patterns can be generated by more than one antenna such as is shown in  FIGS. 5, 7, 9, 10, 11 and 12 . 
     In general, the adaptive interpolation method works with all “staggered” pilot patterns which describes all shapes other than a square, which does not work. A perfect diamond shape, which is the most favorable shape, is a special case of a staggered pilot pattern. Another example of a pattern which would work is a “kite” pattern where the pilots are spread further apart in one direction than the other. 
     More generally, in  FIGS. 4A to 11 , in each sub-frame, pilots are transmitted by part of the sub-carriers in at least two non-contiguous OFDM symbols by at least one transmit antenna. The pilot sub-carriers in the first OFDM symbol and the second OFDM symbol are staggered in the frequency domain. In  FIGS. 5A, 5D, 7A, 7D, 9A and 9D , pilot symbols from all transmit antennas are transmitted through the same non-contiguous OFDM symbols. This arrangement will save the terminal power since only two OFDM symbols are coded to obtain the channel information. 
       FIG. 4A  is a diagram of a single antenna irregular diamond lattice scattered pilot pattern which can used in accordance with an embodiment of the present invention. The overhead associated with this pilot pattern is 1/28 per antenna. Pilot and data symbols are spread over an OFDM sub-frame in a time direction  420  and a frequency direction  422 . Most symbols within the OFDM sub-frame are data symbols  424 . Pilot symbols  426  are inserted in an irregular diamond lattice pattern. In this embodiment, an OFDM sub-frame comprises eight sub-carriers  428  and seven OFDM symbols  430 . 
     As with the scattered pilot pattern in  FIG. 1 , there is first performed a calculation of the channel changes in both the time direction and the frequency direction and a comparison is made as to which direction the channel changes faster. One-dimensional interpolation is then performed in the direction with slower channel change. One-dimensional interpolation is then performed in the direction with faster channel change. 
       FIG. 4B  is a diagram of a single antenna irregular diamond lattice scattered pilot pattern which can used in accordance with an embodiment of the present invention. Though similar to  FIG. 4A , in this case one of the pilots in each diamond lattice is offset by one OFDM symbol position. Thus, the adaptive interpolation method does not require that the scattered pilots line up in either or both of the time direction and the frequency direction. In the case of staggered pilot patterns where the pilots do not line up in either the time direction, the frequency direction, or both, it is more accurate to refer to the “h 1 /h 2  direction” and the “h 3 /h 4  direction” rather than the time direction and the frequency direction. 
       FIG. 5A  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. The overhead associated with this scattered pilot pattern is 1/28 per antenna. In this embodiment, an OFDM frame comprises eight sub-carriers  528  and seven OFDM symbols  530 . 
     Pilot and data symbols are spread over an OFDM frame in a time direction  420  and a frequency direction  522 . Most symbols within the OFDM frame are data symbols  524 . Pilot symbols  526  are inserted in an irregular diamond lattice pattern. 
     As with the scattered pilot pattern in  FIG. 1 , there is first performed a calculation of the channel changes in both the time direction and the frequency direction and a comparison is made as to which direction the channel changes faster. One-dimensional interpolation is then performed in the direction with slower channel change. Using these measurements, one-dimensional interpolation is then performed in the direction with faster channel change. 
       FIGS. 5B, 5C and 5D  are three other examples of scattered pilot patterns which can be generated according to this embodiment. 
       FIG. 6  is a diagram of a single antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 7A  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 7B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 7C  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 7D  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 8  is a diagram of a single antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 9A  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 9B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 9C  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 9D  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 10A  is a diagram of a one antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 10B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 11A  is a diagram of a one antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 11B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 12A  is a diagram of a one antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
       FIG. 12B  is a diagram of a four antenna irregular diamond lattice scattered pilot pattern which can be used in accordance with an embodiment of the present invention. 
     For the purposes of providing context for embodiments of the invention for use in a communication system,  FIGS. 13-17  will now be described. As will be described in more detail below, the method of the present invention can, in one embodiment, be implemented through means of the channel estimation logic of a conventional OFDM receiver (see channel estimation  96  in  FIG. 17 ). 
       FIG. 13  shows a base station controller (BSC)  10  which controls wireless communications within multiple cells  12 , which cells are served by corresponding base stations (BS)  14 . In general, each base station  14  facilitates communications using OFDM with mobile and/or wireless terminals  16 , which are within the cell  12  associated with the corresponding base station  14 . The movement of the mobile terminals  16  in relation to the base stations  14  results in significant fluctuation in channel conditions. As illustrated, the base stations  14  and mobile terminals  16  may include multiple antennas to provide spatial diversity for communications. 
     A high level overview of the mobile terminals  16  and base stations  14  upon which aspects of the present invention may be implemented is provided prior to delving into the structural and functional details of the preferred embodiments. With reference to  FIG. 14 , a base station  14  is illustrated. The base station  14  generally includes a control system  20 , a baseband processor  22 , transmit circuitry  24 , receive circuitry  26 , multiple antennas  28 , and a network interface  30 . The receive circuitry  26  receives radio frequency signals bearing information from one or more remote transmitters provided by mobile terminals  16  (illustrated in  FIG. 13 ). A low noise amplifier and a filter (not shown) may cooperate to amplify and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
     The baseband processor  22  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor  22  is generally implemented in one or more digital signal processors (DSPs) or application-specific integrated circuits (ASICs). The received information is then sent across a wireless network via the network interface  30  or transmitted to another mobile terminal  16  serviced by the base station  14 . 
     On the transmit side, the baseband processor  22  receives digitized data, which may represent voice, data, or control information, from the network interface  30  under the control of control system  20 , and encodes the data for transmission. The encoded data is output to the transmit circuitry  24 , where it is modulated by a carrier signal having a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas  28  through a matching network (not shown). Various modulation and processing techniques available to those skilled in the art are used for signal transmission between the base station and the mobile terminal. 
     With reference to  FIG. 15 , a mobile terminal  16  configured according to one embodiment of the present invention is illustrated. Similarly to the base station  14 , the mobile terminal  16  will include a control system  32 , a baseband processor  34 , transmit circuitry  36 , receive circuitry  38 , multiple antennas  40 , and user interface circuitry  42 . The receive circuitry  38  receives radio frequency signals bearing information from one or more base stations  14 . A low noise amplifier and a filter (not shown) may cooperate to amplify and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
     The baseband processor  34  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. The baseband processor  34  is generally implemented in one or more digital signal processors (DSPs) and application specific integrated circuits (ASICs). 
     For transmission, the baseband processor  34  receives digitized data, which may represent voice, data, or control information, from the control system  32 , which it encodes for transmission. The encoded data is output to the transmit circuitry  36 , where it is used by a modulator to modulate a carrier signal that is at a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas  40  through a matching network (not shown). Various modulation and processing techniques available to those skilled in the art are used for signal transmission between the mobile terminal and the base station. 
     In OFDM modulation, the transmission band is divided into multiple, orthogonal carrier waves. Each carrier wave is modulated according to the digital data to be transmitted. Because OFDM divides the transmission band into multiple carriers, the bandwidth per carrier decreases and the modulation time per carrier increases. Since the multiple carriers are transmitted in parallel, the transmission rate for the digital data, or symbols, on any given carrier is lower than when a single carrier is used. 
     OFDM modulation utilizes the performance of an Inverse Fast Fourier Transform (IFFT) on the information to be transmitted. For demodulation, the performance of a Fast Fourier Transform (FFT) on the received signal recovers the transmitted information. In practice, the IFFT and FFT are provided by digital signal processing carrying out an Inverse Discrete Fourier Transform (IDFT) and Discrete Fourier Transform (DFT), respectively. Accordingly, the characterizing feature of OFDM modulation is that orthogonal carrier waves are generated for multiple bands within a transmission channel. The modulated signals are digital signals having a relatively low transmission rate and capable of staying within their respective bands. The individual carrier waves are not modulated directly by the digital signals. Instead, all carrier waves are modulated at once by IFFT processing. 
     In operation, OFDM is preferably used for at least down-link transmission from the base stations  14  to the mobile terminals  16 . Each base station  14  is equipped with “n” transmit antennas  28 , and each mobile terminal  16  is equipped with “m” receive antennas  40 . Notably, the respective antennas can be used for reception and transmission using appropriate duplexers or switches and are so labeled only for clarity. 
     With reference to  FIG. 16 , a logical OFDM transmission architecture will be described. Initially, the base station controller  10  will send data to be transmitted to various mobile terminals  16  to the base station  14 . The base station  14  may use the channel quality indicators (CQIs) associated with the mobile terminals to schedule the data for transmission as well as select appropriate coding and modulation for transmitting the scheduled data. The CQIs may be directly from the mobile terminals  16  or determined at the base station  14  based on information provided by the mobile terminals  16 . In either case, the CQI for each mobile terminal  16  is a function of the degree to which the channel amplitude (or response) varies across the OFDM frequency band. 
     Scheduled data  44 , which is a stream of bits, is scrambled in a manner reducing the peak-to-average power ratio associated with the data using data scrambling logic  46 . A cyclic redundancy check (CRC) for the scrambled data is determined and appended to the scrambled data using CRC adding logic  48 . Next, channel coding is performed using channel encoder logic  50  to effectively add redundancy to the data to facilitate recovery and error correction at the mobile terminal  16 . Again, the channel coding for a particular mobile terminal  16  is based on the CQI. In some implementations, the channel encoder logic  50  uses known Turbo encoding techniques. The encoded data is then processed by rate matching logic  52  to compensate for the data expansion associated with encoding. 
     Bit interleaver logic  54  systematically reorders the bits in the encoded data to minimize the loss of consecutive data bits. The resultant data bits are systematically mapped into corresponding symbols depending on the chosen baseband modulation by mapping logic  56 . Preferably, Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Key (QPSK) modulation is used. The degree of modulation is preferably chosen based on the CQI for the particular mobile terminal. The symbols may be systematically reordered to further bolster the immunity of the transmitted signal to periodic data loss caused by frequency selective fading using symbol interleaver logic  58 . 
     At this point, groups of bits have been mapped into symbols representing locations in an amplitude and phase constellation. When spatial diversity is desired, blocks of symbols are then processed by space-time block code (STC) encoder logic  60 , which modifies the symbols in a fashion making the transmitted signals more resistant to interference and more readily decoded at a mobile terminal  16 . The STC encoder logic  60  will process the incoming symbols and provide “n” outputs corresponding to the number of transmit antennas  28  for the base station  14 . The control system  20  and/or baseband processor  22  as described above with respect to  FIG. 14  will provide a mapping control signal to control STC encoding. At this point, assume the symbols for the “n” outputs are representative of the data to be transmitted and capable of being recovered by the mobile terminal  16 . 
     For the present example, assume the base station  14  has two antennas  28  (n=2) and the STC encoder logic  60  provides two output streams of symbols. Accordingly, each of the symbol streams output by the STC encoder logic  60  is sent to a corresponding IFFT processor  62 , illustrated separately for ease of understanding. Those skilled in the art will recognize that one or more processors may be used to provide such digital signal processing, alone or in combination with other processing described herein. The IFFT processors  62  will preferably operate on the respective symbols to provide an inverse Fourier Transform. The output of the IFFT processors  62  provides symbols in the time domain. The time domain symbols are grouped into frames, which are associated with a prefix by prefix insertion logic  64 . Each of the resultant signals is up-converted in the digital domain to an intermediate frequency and converted to an analog signal via the corresponding digital up-conversion (DUC) and digital-to-analog (D/A) conversion circuitry  66 . The resultant (analog) signals are then simultaneously modulated at the desired RF frequency, amplified, and transmitted via the RF circuitry  68  and antennas  28 . Notably, pilot signals known by the intended mobile terminal  16  are scattered among the sub-carriers. The mobile terminal  16 , which is discussed in detail below, will use the pilot signals for channel estimation. 
     Reference is now made to  FIG. 17  to illustrate reception of the transmitted signals by a mobile terminal  16 . Upon arrival of the transmitted signals at each of the antennas  40  of the mobile terminal  16 , the respective signals are demodulated and amplified by corresponding RF circuitry  70 . For the sake of conciseness and clarity, only one of the two receive paths is described and illustrated in detail. Analog-to-digital (A/D) converter and down-conversion circuitry  72  digitizes and downconverts the analog signal for digital processing. The resultant digitized signal may be used by automatic gain control circuitry (AGC)  74  to control the gain of the amplifiers in the RF circuitry  70  based on the received signal level. 
     Initially, the digitized signal is provided to synchronization logic  76 , which includes coarse synchronization logic  78 , which buffers several OFDM symbols and calculates an auto-correlation between the two successive OFDM symbols. A resultant time index corresponding to the maximum of the correlation result determines a fine synchronization search window, which is used by fine synchronization logic  80  to determine a precise framing starting position based on the headers. The output of the fine synchronization logic  80  facilitates frame acquisition by frame alignment logic  84 . Proper framing alignment is important so that subsequent FFT processing provides an accurate conversion from the time domain to the frequency domain. The fine synchronization algorithm is based on the correlation between the received pilot signals carried by the headers and a local copy of the known pilot data. Once frame alignment acquisition occurs, the prefix of the OFDM symbol is removed with prefix removal logic  86  and resultant samples are sent to frequency offset correction logic  88 , which compensates for the system frequency offset caused by the unmatched local oscillators in the transmitter and the receiver. Preferably, the synchronization logic  76  includes frequency offset and clock estimation logic  82 , which is based on the headers to help estimate such effects on the transmitted signal and provide those estimations to the correction logic  88  to properly process OFDM symbols. 
     At this point, the OFDM symbols in the time domain are ready for conversion to the frequency domain using FFT processing logic  90 . The results are frequency domain symbols, which are sent to processing logic  92 . The processing logic  92  extracts the scattered pilot signal using scattered pilot extraction logic  94 , determines a channel estimate based on the extracted pilot signal using channel estimation logic  96 , and provides channel responses for all sub-carriers using channel reconstruction logic  98 . In order to determine a channel response for each of the sub-carriers, the pilot signal is essentially multiple pilot symbols that are scattered among the data symbols throughout the OFDM sub-carriers in a known pattern in both time and frequency. Examples of scattering of pilot symbols among available sub-carriers over a given time and frequency plot in an OFDM environment are found in PCT Patent Application No. PCT/CA2005/000387 filed Mar. 15, 2005 assigned to the same assignee of the present application. Continuing with  FIG. 17 , the processing logic compares the received pilot symbols with the pilot symbols that are expected in certain sub-carriers at certain times to determine a channel response for the sub-carriers in which pilot symbols were transmitted. The results are interpolated to estimate a channel response for most, if not all, of the remaining sub-carriers for which pilot symbols were not provided. The actual and interpolated channel responses are used to estimate an overall channel response, which includes the channel responses for most, if not all, of the sub-carriers in the OFDM channel. 
     The frequency domain symbols and channel reconstruction information, which are derived from the channel responses for each receive path are provided to an STC decoder  100 , which provides STC decoding on both received paths to recover the transmitted symbols. The channel reconstruction information provides equalization information to the STC decoder  100  sufficient to remove the effects of the transmission channel when processing the respective frequency domain symbols. 
     The recovered symbols are placed back in order using symbol de-interleaver logic  102 , which corresponds to the symbol interleaver logic  58  of the transmitter. The de-interleaved symbols are then demodulated or de-mapped to a corresponding bitstream using de-mapping logic  104 . The bits are then de-interleaved using bit de-interleaver logic  106 , which corresponds to the bit interleaver logic  54  of the transmitter architecture. The de-interleaved bits are then processed by rate de-matching logic  108  and presented to channel decoder logic  110  to recover the initially scrambled data and the CRC checksum. Accordingly, CRC logic  112  removes the CRC checksum, checks the scrambled data in traditional fashion, and provides it to the de-scrambling logic  114  for de-scrambling using the known base station de-scrambling code to recover the originally transmitted data  116 . 
     In parallel to recovering the data  116 , a CQI, or at least information sufficient to create a CQI at the base station  14 , is determined and transmitted to the base station  14 . As noted above, the CQI may be a function of the carrier-to-interference ratio (CR), as well as the degree to which the channel response varies across the various sub-carriers in the OFDM frequency band. The channel gain for each sub-carrier in the OFDM frequency band being used to transmit information is compared relative to one another to determine the degree to which the channel gain varies across the OFDM frequency band. Although numerous techniques are available to measure the degree of variation, one technique is to calculate the standard deviation of the channel gain for each sub-carrier throughout the OFDM frequency band being used to transmit data. 
       FIG. 18  is a block diagram of one embodiment of the present invention. In this embodiment, the present invention is shown being implemented within channel estimation logic  96  of  FIG. 17  with the conventional aspects of channel estimation logic  96  being shown in dotted outline for ease of reference. Persons skilled in the art will appreciate that the present invention could be implemented as a separate logical component as well. 
     Shown is time direction channel calculator  127  which performs the calculation of channel change in the time direction. Frequency direction channel calculator  129  performs the calculation of channel change in the frequency direction. As explained above, the preferred calculation is the inner product of the two pilot assisted channel estimates being compared. Though time direction channel calculator  127  is shown as being illustrated to the right of frequency direction channel calculator  129 , this does not mean that the time direction channel calculation is necessarily to be performed first or that the calculations cannot be performed simultaneously. Either calculation can be performed first, or both can be performed simultaneously. Channel direction comparator  131  compares the results of the calculations performed by both direction channel calculator  127  and frequency direction channel calculator  129  for the purpose of comparing and ascertaining which channel direction, time or frequency, changes slower. Channel direction selector  133  selects which of the two directions changes slower. Block  135  is utilized to interpolate, first in the direction of slower change, and then in the direction of faster change, in accordance with conventional means. 
     In operation, time direction channel calculator  127  receives two pilot assisted channel estimates and performs the calculation of channel change in the time direction. Frequency direction channel calculator  129  performs the calculation of channel change in the frequency direction though these two calculations can be performed in different order or simultaneously. Channel direction comparator  131  compares the results of the calculations performed by both direction channel calculator  127  and frequency direction channel calculator  129  and compares which channel direction, time or frequency, changes slower. Channel direction selector  133  selects the direction of slower change and interpolation is then performed by block  135  in that direction first, and then in the direction of faster change in accordance with conventional means. 
       FIGS. 13 to 18  each provide a specific example of a communication system or elements of a communication system that could be used to implement embodiments of the invention. It is to be understood that embodiments of the invention can be implemented with communications systems having architectures that are different than the specific example, but that operate in a manner consistent with the implementation of the embodiments as described herein. 
     Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Metadata:
Filing Date: 20190606
Publication Date: 20191112
Grant Date: 20191112
Priority Date: 20050823
Inventors: MA, JIANGLEI
JIA, MING
TONG, WEN
ZHU, PEIYING
ZHANG, HANG
XU, HUA
YU, DONGSHENG
Assignee: APPLE INC
CPC Classifications: [{"code": "H04L5/0007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0023", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0003", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L5/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2647", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0009", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/325", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0232", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0618", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L5/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0003", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L5/0023", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0009", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L25/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0226", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0618", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/325", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0048", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0226", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0048", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/325", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0009", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L27/2611", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L27/2613", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2647", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0618", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B7/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2626", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0023", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2602", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0232", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0003", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B7/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2602", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L27/26134", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L5/0048", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/26134", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L27/2602", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 37771198