Systems and methods for coordinating the coverage and capacity of a wireless base station

WO 2006/107656 PCT/US2O06/011272

SYSTEMS AND METHODS FOR COORDINATING THE COVERAGE AND CAPACITY OF A WIRELESS BASE STATION

TECHNICAL FIELD

[0001] This Invention relates to wireless communication and more particularly to systems and methods for increasing base station coverage and capacity in a wireless network, and even more particularly to such methods and systems for placement of wireless transceivers within a communication network. WO 2006/107656 PCT/US2006/011272

SYSTEMS AND METHODS FOR COORDINATING THE COVERAGE AND

CAPACITY OF A WIRELESS BASE STATION

BACKGROUND OF THE INVENTION

[0002] One problem experienced in wireless communication systems is locating base stations. Once a base station (transmitter/receiver) is positioned in a coverage area it is important to be able to set its respective parameters in order to provided the desired coverage or capacity.

[0003] In this context, coverage is the geographical area covered by the signals to or From the base station while capacity relates to the amount of data that can pass through the base station to or from mobile devices. Base stations can be optimized for either coverage area or capacity (throughput). Typically, such optimization has been accomplished by using a sophisticated set of tools that are available to the wireless network designer. These tools would provide signal propagation models to the designer for use in calculating coverage areas for a particular base station. The designer would also estimate the interference that could result with respect to mobile devices communicating with a different base station some distance away, so these may or may not be on the same channel.

[0004] In some wireless networks the various base stations would use different channels or frequencies to avoid interference issues. Wireless network frequency planning is used to avoid, or minimize, such interference problems between adjacent and nearby base stations.

[0005] In newer wireless systems, such as, for example, OFDM and OFDMA, the tendency is to overlap frequencies and channels across base stations and to eliminate interference by assigning different combinations of sub-channels (sub-carriers) to different mobile devices communicating at the same time. These modulation schemes allow variable data rates and variable amounts of robustness in terms of being able to tolerate the interference. The ideal system is one in which a base station can serve a high number of mobile devices with no interference between devices. In order to achieve such an ideal system it is important that each communicating mobile device has a strong 2 WO 2006/107656 PCTZTJS2006/011272 signal. If on the other hand there are two mobile devices each on the edge of coverage with two base stations and if propagation were uniform those mobile devices would most likely experience interference. This interference would reduce the data rate for those devices in order to protect the integrity of the data.

[0006] Turing to the problem of location of a new transmitter/receiver (herein called a transceiver) the network designer, as discussed above, decides on a location, has the transceiver erected and installed and then tunes it up by adjusting the power level, the elevation angle of the antenna, etc. in accordance with the precalculated plan for this transceiver. Once these adjustments are made, the transceiver is turned on and “sees what actually happens”. The technician can then readjust the power levels, adjust the down tilt of the antenna, and possibly swap out the antenna with an antenna having a different azimuth angle. If the transceiver continues to cause interference, or not properly cover the designated area network adjustments might have to be made, or the power level reduced further. In some instances the adjacent base stations also need to be read. 3 WO 2006/107656 PCT/US2006/011272

BRIEF SUMMARY OP THE INVENTION

[0007] A communications base station is installed at a selected new location and the base station, prior to going "on line” monitors the wireless traffic from other base stations within interference range of the new base station’s coverage area.

The new base station also monitors the wireless traffic between mobile devices within its coverage area and these other base stations. Based upon these monitored conditions, as well as other known conditions, the new base station then determines the transmitting parameter configuration it should apply in order to achieve a desired optimization between capacity and coverage area.

[0008] After the new base station is on line, a central control can monitor the entire network to determine if any additional changes are necessary and if so the new transceiver, or any other transceiver, can be instructed to monitor itself with respect to interference and to take corrective action to improve overall network coverage and capacity.

[0009] In one embodiment, operating power levels are gradually raised as the new base station comes on line so as to minimize interference. In addition, if desired, the new base station can automatically adjust its antenna beams in elevation, pointing angle and beam width.

[0010] In one embodiment, the new base station would determine the most optimum operating parameters for its use, and if those parameters cause interference in the network then a central control will assist in the adjustment of the network to achieve the optimization of the entire network, [0011] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It 4 WO 2006/107656 FCT/US20O6/O11272 should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 5 WO 2006/107656 PCT/US20O6/011272

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [0013] FIGURE 1A shows one embodiment of a wireless network where a base station is being added; [0014] FIGURE IB is a chart illustration of the before and after characteristics at certain locations within the coverage area of the wireless network; [0015] FIGURE 2 is a flow chart illustrating one embodiment of die invention; and [0016] FIGURE 3 is an illustration of one embodiment of the invention demonstrating coverage areas. 6 WO 2006/107656 PCT/XJS2006/011272

DETAILED DESCRIPTION OF ΊΉΕ INVENTION

[0017] FIGURE 1A shows wireless network 10 initially having one base station 11 with coverage area defined by dotted line 12. Transmission and other control to/from base station 11 is controlled by base station controller 121 in conjunction with central control (NOC) 120 which could be co-located with a base station, if desired. Contained within base station controller 121 is a database and at least one software program which controls transmission to/from the base station as is now well known. As will be seen, while transmission from base station 11 can, in theory, reaches out to point 104, transmissions to and from that location would most probably be unsatisfactory because of low energy. Since mobile devices, such as cell phones, PDAs, computers, two-way pagers and the like, do not transmit with as much energy as does a base station, most wireless devices would not be able to transmit as far as does the base station and thus the actual coverage area would be even less than shown by dotted fine 12.

[0018] hi Figure 1 A, there are three points of interest, 101,102, and 103, that will be examined. However, the concepts that we will be discussing are applicable over the entire coverage area, varying only in degree. Also note that while certain network types, such as OFDM and OFDMA networks, will be discussed, the concepts discussed herein can be applied to many network types.

[0019] An OFDM network contains many (256-1024 being typical) orthogonal carriers. In such a system, subcarrier aggregations are formed (typically in the order of 16 to 32) for each communication connection in order to decrease interference and thus increase capacity (throughput). In order to support many more active users, the subcairiers may be time-shared and reassigned to different mobile stations on a frame by frame basis with a typical frame being 5 ms. ha such systems, it is possible for several mobile devices to share some (but not all) of the carriers used by the other devices. If the subcarriers that make up a particular connection are properly selected, interference between the mobile devices is reduced to a minimum. A more complete description of an OFDM system is contained in “OFDM for Wireless Multimedia Communications” by Richard D. J. Van Nee and Ramjee Prasad (ISBN 0890065306) which is hereby incorporated by reference herein, ha addition, the 7 WO 2006/107656 PCT/US2006/0Π272 following references, which are hereby incorporated by reference herein, are useful for calculating propagation loss: “Field Strength and Its Variability in VHF and UHF Land-Mobile Radio Service/5 by Yoshihisa Okumura, et at, Review of the Electrical Communications Laboratory, VoL 16, No. 9-10, September-October 1968 and Hata “Empirical formula for propagation loss in Land Mobile radio services,” IEEE Transactions on Vehicular Technology, Vol. 29, No. 3, Aug. 1980.

[0020] When a need arises for a new base station, either by an increase in wireless usage in an area or by the construction of a structure blocking existing transmissions, engineering calculations are made to determine the most effective possible sites. These calculations take into account a myriad of factors, including the amount of added capacity and amount of added coverage area desired. However, while the engineering factors are important, other factors, such as availability of land and the ability to obtain governmental and regulatory approvals must also be considered. Once the new location, for example location 110, FIGURE 1, is decided upon for abase station (transceiver), the base station is constructed at that site.

[0021] The procedure that has been followed in the past when a base station is ready to go online is that the antennas are set to achieve the calculated distances and radiation pattern and the transceiver “lights up” (goes online) and begins to transmit. Calculations are then made as to interference and other factors. Adjustments are than made to the power levels, frequencies are changed, antenna tilt (either physically or electronically) as well as other factors are adjusted to make sure the new base station does not interfere with, for example, transmission to/from base station 11. Often the results are confirmed by extensive and tedious drive testing.

[0022] Based upon the concepts discussed herein, new base station 13 is constructed at location 110, but prior to coming online, new base station (NBS) 13 performs at least two functions. The first function is that it monitors the wireless traffic from other base stations within interference range of the coverage area of the transceiver. The second function performed is to monitor wireless traffic between the mobile devices within its coverage area of its base station and other base stations to determine what level of coverage is available. 8 WO 2006/107656 PCT/US2006/011272 [0023] For example, as shown in FIGURE IB, base station 13 would monitor traffic in the region of 101 and find that there is good coverage from existing base station 11 and into area 101 there would possibly be interference between the two base stations.

[0024] Base station 13 would monitor region 102 and determine that there is marginal coverage from transceiver 11 that with the conclusion area 102 is an area that base station 13 should cover. Base station 13 also looks at region 103 and determines that wireless devices in that area are not being properly served with the conclusion that area 103 would be a good coverage area for transceiver 13.

[0025] This procedure is followed for a period of time until new base station 13 understands the coverage areas and the transmissions from different communication devices within its area. At that point, base station 13 “lights up” and goes online. Once online, base station 13 can monitor the traffic to see if, in fact, there is an unanticipated interference. In some situations central control 120, which can be part of any base station or could be a separate stand alone control center, can receive signals and measurements from a plurality of base stations and can operate to send adjustment commands to one or more of the base stations asking the base stations to change their coverage area power level, frequency, or even their mode of operation.

Note that because traffic patterns change by time of day and between weekday and weekend, base station 13 could be setup as an average “best effort” configuration. Also note that base station 13 (or any base station using the concepts discussed herein) can maintain in memory sets of parameters suitable for such different times (busy hours, day/night, weekday, weekend, emergency, etc.) and can then adjust the parameter of the BS to best suit those times.

[0026] After new base station 13 has come online other base stations could, if desired, perform the same monitoring functions and adjust themselves so as to optimize the network. This optimization can be on a periodic basis or under certain triggers such as when a certain number of calls are dropped or when a certain number of mobile stations report high interference levels. Control would be.required between base 9 WO 2006/107656 FCT/US2006/011272 stations so that the base stations do not interact with each other to cause a destabilization of the network [0027] FIGURE 2 shows one embodiment 20 of a flow chart illustrating the “plug and play” nature of the addition of a new base station and illustrates one example of bringing a new base station on line. Process 201 controls the New Base Station (NBS) so that it tunes to all the base station emissions within the coverage area. The NBS .tunes to the other BS frequencies and/or timeslots. This is done to begin the mapping process with respect to signals and interference in and around the NRS. The NBS measures received power from all base stations where the power is above the noise threshold or other set thresholds. This is necessary so that the NBS knows what devices are in its coverage area and what frequencies are involved. Some of the information obtained by the NBS comes from central control (NOC) 120 and is used to calculate: a a path loss to the NBS from each base station (BS); b. a predicted path loss of a mobile station (MS) within the NBS range to each BS (formula); and c. a path loss (PL) vs distance function (this may be angle dependant) for an assumed MS in communication with the NBS (formula, model).

[0028] Process 202 measures the signal levels of each channel at each base station. Λ log is made of the frequencies and power levels that are received at the NBS from the nearby BSs.

[0029] Process 203 rank orders the signal levels by power or by any other parameter desired. For example, a power rank order list is compiled which provides a first indication of what channels the BS may select, the weakest signals being the most likely selections.

[0030] Process 204 tunes and monitors transmission mobile station transmissions tor X hours and associates each mobile station with a particular base station. A data set is collected by monitoring and aggregating the received powers from a host of MS. The NBS knows from the NOC the channels and their associated BS 10 WO 2006/107656 FCT/US2006/011272 locations. This monitoring is so that the new base station gets a picture of the transmissions to and from mobile stations and who they are communication with and can take from a few hours to several days to obtain a fair picture of wireless traffic. The actual time depends on the accuracy required.

[0031] Process 205 computes the mobile station receive signal level distribution for each base station by calculating the power received at a MS and from a MS and BS at any given distance from the NBS. The MS associated with each BS is knowable because of unique frequencies, timeslots and other pilot addressing schemes as provided by a standard (e.g., IEEE 802.16a). For each BS there will be a distribution of MS signal levels due to their various locations. The NBS calculates the expected maximum distance that a MS can be from the NBS based on the NBS potential available power antenna gain, height, terrain parameters, etc. The NBS also calculates the expected distance of a MS from the NBS where the Signal to Interference Ratio (SIR) = 1. That is a MS receives equal power from the NBS and the strongest existing BS on the same channel.

[0032] This is shown by illustration 30, FIGURE 3. The strongest BS is BS (1) and range A’-B’ is the useable range where SIR ~ 1 (ie. the signal and interference are equal). Range C would be the range of the NBS if interference were not a factor. Note that range C will vary based on the transmitting parameters, (power, frequency, tilt, pattern, polarization, etc.) of the NBS, as well as terrain, foliage, buildings, etc.

[0033] In process 206 the operator has previously input a set of goals (e.g., increase capacity in a certain area). This calculates into ideal settings for constant W, Y and Z to be used in the signal flow below. Process 206 adjusts the NBS in accordance with these system goals or requirements. This step requires a service provider assisted goal, for example. A goal could he to: Expand the range until SIR at mobile equals X dB (0, +3, +6, negative is generally not useful as the other BS should handle the MS unless that BS is full). An alternative goal could be to: Expand the range until a predetermined amount of traffic is acquired within a given range. Further optimization can be achieved by adjusting sector pattern and downtilt For example, the NBS can 11 WO 2006/107656 PCT/US20O6/O11272 expand in beamwidth to increase traffic or it can increase downtilt to reduce interference inside the coverage area.

[0034] Process 207 determines if there is a channel where mobile station and signals are below a certain dB level Y. The parameter Y may be set very low so that the most ideal channel is found. If the answer is yes, then at least temporarily base station 13 assigns itself that channel via process 208 and could at this point come online process 404, at least with respect to that channel. In this context, it could be a channel or a set of sub-channels or any combination thereof.

[0035] If the criteria of process 207 cannot be met, a reduced requirement is tested. In process 210 if certain percentage W of the MS meet the criteria, that channel is assigned (process 2Π) and the BS brought online at process 209.

[0036] If the answer is no in process 210 (i.e., even the reduced criteria are not met) then process 212 determines if there is a subset of channels available. If the answer at process 210 is yes, the base station will assign itself those subsets via process 213, and a reduced capacity HBS is brought online (process 209). If the answer is no, at process 212 then a new set of requirements are rendered (new Y, Z and W in our example) via process 214 and processes 406 - 414 are repeated until the NBS is operational.

[0037] The new requirement could, for example, be a change of transmission parameters from other BSs under control of NOC 120 by adjusting BS power and antenna parameters to reduce interference or increase system capacity. Also, the NBS can refine its estimate of pathloss based on ranging information from MS after it “lights up”. This is based on the fact that a MS will choose a BS based on the strongest pilot signal the MS receives, the NBS can determine from rime of arrival data (distributions) the range of actual MS. Accordingly, the NBS can adjust power and/or antenna parameters to more closely match the desired coverage.

[0038] The logic flow may readily he extended (line 220) after the NBS is turned on to monitor, for example, the increased traffic versus the transceiver signal power or versus antenna downtilt. 12 WO 2006/107656 FCT/US2006/011272 [0039] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 13