Method of Determining True Error Vector Magnitude in a Wireless Lan

• US 20090316589A1
• Filed: 05/27/2005
• Published: 12/24/2009
• Est. Priority Date: 05/27/2004
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Synad Technologies Ltd. (STMicroelectronics NV)
• Inventors: Shafeeu, Hassan
• Granted Patent: US 8,116,363 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• 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 of, comprising the steps of:

(a) supplying a plurality of test signals, each having a test signal amplitude and phase, to a transmitter arrangement for a wireless local area network (WLAN);

(b) obtaining a data distribution of the measured amplitude and phases of the test signals;

(c) allocating each of the measured amplitude and phase values to a one of a finite plurality of data groups;

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

(e) calculating a true Error Vector Magnitude (EVM), resulting 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 said 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 said measured values in each data group further comprises:

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

calculating the true 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 any preceding claim 1, wherein each of the plurality of test signals includes data modulated onto a sub-carrier of an Orthogonal Frequency Division Muliplexed (OFDM) carrier.

7. 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.

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

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

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

9. The method of claim 8, 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.

10. A method, comprising:

supplying a plurality of test signals, each having a test signal amplitude and phase, to a transmitter arrangement of a wireless local area network (WLAN);

obtaining a data distribution of the measured amplitude and phases of the test signals;

allocating each of the measured amplitude and phase values to a one of a finite plurality of data groups;

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

calculating, from the said 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.

11. The method of claim 10, wherein determining an average of the measured amplitude comprises calculating the position of the mean of the values in each of the finite plurality of data groups.

12. A method, comprising:

associating each point in a communications constellation to an ideal reception location in a constellation diagram, the ideal reception location being due only to effects of IQ imbalance but not phase noise;

allocating a measured communication amplitude and phase value for each one of a plurality of received actual signals, affected by both IQ imbalance and phase noise, to a one of a finite plurality of data groups;

calculating a spread within each of the data groups with respect to an associated one of the ideal reception locations;

estimating an Error Vector Magnitude (EVM) from the calculated spread of each data group.

13. The method of claim 12 wherein calculating the spread comprises calculating a standard deviation.

14. The method of claim 12 wherein estimating comprises averaging standard deviations for each data group.

15. The method of claim 12 wherein calculating the spread comprises calculating a variance.