Method for estimating the downlink capacity in a spread spectrum wireless communications system
View Patent ↗The per sector or per cell downlink capacity in a spread spectrum wireless network is determined using a single test mobile that is operating within a background of simulated co-channel interference being broadcast in each sector by all cell sites in the network whose capacity is of interest. From all sectors, an Orthogonal Channel Noise Simulator (OCNS) generates a multiple number of calibrated test signals, which are aggregated and broadcast downlink, where each transmitted test signal simulates the downlink power transmitted to a live mobile. Each component test signal in the aggregated OCNS output transmitted in each sector is a sample of a stochastic process with a set mean and standard deviation that are determined from the mean and standard deviation of the power of a real signal transmitted downlink to the test mobile as it is moved around the network's coverage area. The capacity of the sector is determined by increasing the number of test signals in each aggregated OCNS output until measurable performance is compromised.
1. A method of determining capacity in a wireless network in which plural signals are transmitted on a shared downlink channel to plural mobiles within a coverage area of the network, the method comprising:
a) transmitting, from a first base station, a real signal on the downlink channel to a test mobile as it is moved on a test route within the network's coverage area;
b) determining a mean and a variance of the real signal as it is being transmitted on the downlink channel while the test mobile moves on the test route;
c) transmitting, from the first base station, an aggregate of a plurality of first test signals on the downlink channel, each of the plurality of first test signals corresponding to simulated transmission from the first base station to each of a first plurality of mobiles, each first test signal being a sample of a stochastic process that is calibrated to the determined mean and the determined variance of the real signal so that the plurality of first test signals is statistically equivalent to signals transmitted to live mobiles;
d) transmitting, from at least one second base station, an aggregate of a plurality of second test signals on the downlink channel, each of the plurality of second test signals corresponding to simulated transmission from the second base station to each of a second plurality of mobiles, each second test signal being a sample of a stochastic process that is calibrated to the determined mean and the determined variance of the real signal so that the plurality of first test signals is statistically equivalent to signals transmitted to live mobiles;
e) determining whether or not an acceptable performance is indicated by at least one predetermined measurable performance characteristic when the real signal and the first and second pluralities of test signals are being transmitted as the test mobile is being moved on the test route; and
f) if acceptable performance is determined, determining that the downlink channel has the capacity of handling downlink traffic corresponding to at least the first and second pluralities of mobiles.
2. The method of claim 1 wherein if acceptable performance is determined, increasing the first and second pluralities to third and fourth pluralities, respectively, the third and fourth pluralities being a greater number than the first and second pluralities, respectively, and repeating a) through e) to determine whether the acceptable performance is indicated with the third and fourth pluralities, and if acceptable performance is indicated with the third and fourth pluralities, determining that the downlink channel has the capacity of handling downlink traffic to at least this third and fourth pluralities of mobiles.
3. The method of claim 2 wherein if acceptable performance is determined at the third and fourth pluralities, increasing the third and fourth pluralities to successively greater numbers and repeating a) through e) to determine whether acceptable performance is determined for reach successively greater number until a plurality is reached at which unacceptable performance is determined.
4. The method of claim 1 wherein if acceptable performance is not determined, decreasing the first the first and second pluralities to third and fourth pluralities, respectively, the third and fourth pluralities being a smaller number than the and second pluralities, respectively, and repeating a) through e) to determine whether the acceptable performance is indicated with the third and fourth pluralities, and if acceptable performance is determined, determining that the downlink channel has the capacity of handling downlink traffic to at least this third and fourth pluralities of mobiles.
5. The method of claim 4 wherein if acceptable performance is not determined at the third and fourth pluralities, decreasing the third and fourth pluralities to successively smaller numbers and repeating a) through e) to determine whether acceptable performance is determined for each successively smaller greater number until a plurality is reached at which acceptable performance is determined.
6. The method of claim 1 wherein the at least one predetermined performance criteria is at least one of an average downlink error rate being greater than a predetermined error rate; and a percentage of time that a downlink amplifier is in an overload state being greater than a predetermined percent.
7. The method of claim 1 , wherein each first test signal is a sample of a stochastic process that is calibrated to the determined mean and the determined variance of the real signal so that a downlink amplifier is unable to determine a difference between broadcasting a plurality of signals to live mobiles and transmitting the aggregate of the plurality of first test signals on the downlink channel.