Method of determining true error vector magnitude in a wireless LAN

• US 8,116,363 B2
• Filed: 05/27/2005
• Issued: 02/14/2012
• Est. Priority Date: 05/27/2004
• Status: Expired due to Fees

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Synad Technologies Ltd. (STMicroelectronics NV)
• Inventors: Shafeeu, Hassan
• Primary Examiner(s): Rao, Seema S
• Assistant Examiner(s): HUYNH, KHOA B
• Application Number:
  US11/597,604
• Publication Number:
  US 20090316589A1
• Time in Patent Office: 2,454 Days
• Field of Search: None
• US Class Current: 375/227
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems
• CPC Class Codes: H04L 27/364 Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels

Abstract

Systematic transmit IQ phase and amplitude imbalances in the transmit chain of a wireless local area network (WLAN) cause a corresponding systematic shift in the roots of a constellation diagram. Additional random phase noise in the transmit chain will cause a further Gaussian distribution of points in the constellation diagram about the systematically shifted roots. This random distribution represents a true error vector magnitude (EVM). By transmitting a known training sequence through the transmit chain, which it is known will be shifted to all of the systematically shifted roots in the constellation diagram, the Gaussian spread around those shifted roots can be analysed to determine the true EVM.

Claims

1. A method, comprising the steps of:

(a) supplying a plurality of test signals to a transmitter arrangement of a wireless local area network (WLAN), each test signal including data modulated onto a sub-carrier of an Orthogonal Frequency Division Multiplexed (OFDM) signal and having a test signal amplitude and phase, each sub-carrier having a predetermined position within a bandwidth of the OFDM signal, the plurality of test signals comprising at least a first test signal and a second test signal, and wherein the position of the sub-carrier for the first test signal and the position of the sub-carrier for the second test signal are symmetrically arranged about the mid-point of the bandwidth of the OFDM signal, and wherein the first and second test signals each comprise a known training sequence of data which cause finite shifts at each point of an ideal signal constellation of the test signal;

(b) measuring an amplitude and phase of the test signals once they have passed through the transmitter arrangement;

(c) allocating each of the measured amplitude and phase values to one of a finite plurality of data groups, wherein the allocation to a data group of the measured amplitude and phase values corresponding to the first test signal is based on the first test signal amplitude and phase and the second test signal amplitude and phase;

(d) determining the spread in the said measured values, within each of the data groups; and

(e) calculating an Error Vector Magnitude (EVM), resulting only from non-systematic effects within the transmitter arrangement, based upon the determined spread of the measured values within the data groups.

2. The method of claim 1, further comprising:

determining an average of the measured amplitude and phase values within each of the data groups; and

calculating, from the average, the magnitude of a systematic error vector which is a result of systematic shifts introduced into the phase and amplitude of a signal passing through the transmitter arrangement, due to IQ imbalances.

3. The method of claim 1, wherein the step of determining the spread in the measured values in each data group further comprises:

calculating the standard deviation of the measured values in each data group; and

calculating the EVM based upon an average of the calculated standard deviations.

4. The method of claim 3, wherein the step of calculating the true EVM further comprises:

determining the mean of the calculated standard deviations for each of the finite plurality of the data groups.

5. The method of claim 2, wherein the step of determining an average of the measured amplitude further comprises calculating the position of the mean of the values in each of the finite plurality of data groups.

6. The method of claim 1, wherein each test signal includes test data modulated onto it using a technique comprising:

Binary Phase Shift Keying (BPSK);

Binary Frequency Shift Keying (BFSK);

Quadrature Amplitude Modulation (QAM), Gaussian Minimum Shift Keying (GMSK), and M-ary Phase Shift Keying (M-PSK),

and wherein the number of data groups is at least in part a consequence of the manner of data modulation.

7. The method of claim 2, wherein the step of determining the spread in the measured values in each data group further comprises:

calculating the standard deviation of the measured values in each data group; and

calculating the EVM based upon an average of the calculated standard deviations.

8. The method of claim 7, wherein the step of calculating the EVM further comprises:

determining the mean of the calculated standard deviations for each of the finite plurality of the data groups.

9. A method, comprising the steps of:

(a) supplying a plurality of test signals to a transmitter, the test signals having an ideal signal constellation;

(b) passing the test signals through the transmitter to produce output test signals for wireless transmission, the output test signals having a shifted signal constellation relative to the ideal signal constellation due to systematic effects of the transmitter;

wherein the test signals comprise a known training sequence of data which causes shifts at each point of the ideal signal constellation to a finite plurality of positions for each point of the shifted signal constellation;

(c) receiving the output test signals affected by non-systematic effects;

(d) measuring an amplitude and phase of the received test signals;

(e) allocating each of the measured amplitudes and phases for the received test signals to one of a finite plurality of data groups each corresponding to one of the finite plurality of positions within the shifted signal constellation;

(f) calculating a spread of the measured amplitudes and phases within each one of the finite plurality of data groups;

(g) estimating an Error Vector Magnitude (EVM) from the calculated spread of each data group, the estimated EVM being solely due to the non-systematic effects.

10. The method of claim 9, further comprising:

determining an average of the measured amplitude and phase values within each of the data groups; and

calculating, from the average, the magnitude of a systematic error vector which is a result of shifts in the shifted signal constellation introduced by systematic effects as the test signal passes through the transmitter.

11. The method of claim 10 wherein the step of determining an average of the measured amplitudes and phases further comprises calculating the position of the mean of the amplitudes and phases in each of the finite plurality of data groups.

12. The method of claim 10 wherein the step of determining the spread in the measured amplitudes and phases in each data group further comprises:

calculating the standard deviation of the measured amplitudes and phases in each data group; and

calculating the EVM based upon an average of the calculated standard deviations.

13. The method of claim 12, wherein the step of calculating the EVM further comprises:

determining the mean of the calculated standard deviations for each of the finite plurality of the data groups.

14. The method of claim 9, wherein the step of calculating the spread in the measured amplitudes and phases in each data group further comprises:

calculating the standard deviation of the measured amplitudes and phases in each data group; and

calculating the EVM based upon an average of the calculated standard deviations.

15. The method of claim 14, wherein the step of calculating the true EVM further comprises:

determining the mean of the calculated standard deviations for each of the finite plurality of the data groups.

16. The method of claim 9, wherein each test signal includes test data modulated onto it using a technique comprising:

Binary Phase Shift Keying (BPSK);

Binary Frequency Shift Keying (BFSK);

Quadrature Amplitude Modulation (QAM), Gaussian Minimum Shift Keying (GMSK), and M-ary Phase Shift Keying (M-PSK),

and wherein the number of data groups is at least in part a consequence of the manner of data modulation.