Source: https://patents.google.com/patent/EP0702462A1/en
Timestamp: 2019-03-25 10:07:39
Document Index: 617561851

Matched Legal Cases: ['art.\n4', 'art 221', 'art 221', 'art 221', 'art 221', 'art 221', 'art 221', 'art 240', 'art 240', 'art 240', 'art 240', 'art 240', 'art 320', 'art 320', 'art 320', 'art 320', 'art 320', 'art 320', 'art 340', 'art 340', 'art 340', 'art 340', 'art 340']

EP0702462A1 - Wireless communication system using distributed switched antennas - Google Patents
Wireless communication system using distributed switched antennas Download PDF
EP0702462A1
EP0702462A1 EP95306066A EP95306066A EP0702462A1 EP 0702462 A1 EP0702462 A1 EP 0702462A1 EP 95306066 A EP95306066 A EP 95306066A EP 95306066 A EP95306066 A EP 95306066A EP 0702462 A1 EP0702462 A1 EP 0702462A1
EP95306066A
EP0702462B1 (en
David John Helmkamp
1994-09-12 Priority to US08/304,319 priority Critical patent/US5628052A/en
1996-03-20 Publication of EP0702462A1 publication Critical patent/EP0702462A1/en
2002-10-16 Publication of EP0702462B1 publication Critical patent/EP0702462B1/en
2002-11-25 Priority to US304319 priority
Increased coverage and macro diversity from a single base station (110) in a wireless communication system by having the base station coupled to N antennas (118A-118D) is described. Increased coverage and macro diversity are achieved by transmitting from the base station (110) N control messages each via one of the antennas (118A-118D), and transmitting a data message addressed to a mobile unit (144) via a particular one of the antennas previously assigned to the mobile unit for an active call. The mobile unit receives the control messages and the data message and analyzes the control messages to identify from the antennas a "best" antenna. The mobile unit (144) then transmits to the base station (110) a new antenna request identifying the best antenna in an uplink control slot of a frame. The uplink control field is associated with the particular one of the antennas. The base station uses the best antenna to transmit subsequent data messages addressed to the mobile unit. A random access technique, to allow mobile units that are going from an inactive status to an active status, is provided by connecting all base station antennas together during non-call-affiliated slots in the uplink portion of the frame.
Typically, a wireless communication system (such as a cellular telephone system) covers a relatively large geographical area. The mobile units (also called, simply, mobiles) in this typical wireless communication system are usually positioned outside of buildings and communicate with base stsations located on towers that are distributed throughout the coverage region. Accordingly, this typical system is called herein an "outdoor" wireless communication system.
The present invention is directed to a system and method of achieving extended coverage in a wireless communication system by having a base station coupled to N antennas rather than by having multiple, expensive base stations. As a result, macro diversity can be implemented in a straightfoward manner, i.e., signal blocking can be minimized during communications by selecting an antenna that has better propagation characteristics to the mobile than the one in current use.
The mobile may be anywhere within the desired coverage area of the system, but outside the area of coverage achievable by a single base station/antenna. Instead of adding additional base station/antenna nodes, as is done in typical systems, the present invention adds additional antennas to a single base station such that for any active, communication channel/slot, the mobile involved in the active call is reachable via the most optimally placed antenna. As the mobile moves through the system area, it listens to the transmissions of all available antennas (radiators) and continuously informs the base station of its "best" choice of available radiators. The base station will then follow the mobile by communicating over the "best" (by the mobilesÆs reckoning) possible link. Thus, increased coverage over a single base station/antenna combination is achieved while also achieving effective macro diversity, i.e., always choosing and using the best link for communication by selecting the best antenna at a mobileÆs current position.
In the present invention, the RF power level is adjustable so as to insure good performance and to minimize co-channel and adjacent channel interference. The present invention facilitates the solution of coverage issues by the addition of multiple antennas per base station (rather than by increasing power). Multiple antennas are also used to overcome fading problems.
In the present invention, channel/frequency selection is achieved by examining the available spectrum and identifying the next available "quiet" channel.
In one embodiment of the present invention, at most one active mobile unit is assigned to each downlink slot and to each uplink slot. In an alternative embodiment, a plurality of active mobile units may be assigned to each downlink slot and to each uplink slot on multiple frequencies. In this alternate embodiment a unique frequency is assigned to each active mobile unit assigned to the same downlink slot and to the same uplink slot.
Figure 1 is a block diagram of a wireless communication system according to a preferred embodiment of the present invention;
Figure 2A is a frame format according to a first embodiment of the present invention;
Figures 2B and 2C are flowcharts depicting the operation of the present invention according to the first embodiment of the present invention;
Figures 3A and 4 are frame formats according to a second embodiment of the present invention;
Figures 3B and 3C are flowcharts depicting the operation of the present invention according to the second embodiment of the present invention; and
Figure 5 is a third embodiment of the present invention showing an extension of the principles disclosed in the first two embodiments to a multi cell wireless communication system.
Figure 1 is a block diagram of a wireless communication system 102 according to a preferred embodiment of the present invention. The wireless communication system 102 covers a geographical area that includes one or more cells 114, each containing one or more sub-cells 116, respectively (the sizes and shapes of the cell 114, and sub-cells 116, are exaggerated in Figure 1 for readability purposes; in practice, each cell 114, generally conforms to the sizes and shapes of the sub-cells 116, respectively, contained therein). A cell is an area of radio coverage for a base station over which a predefined system performance level has been established. A sub-cell is an area of coverage for a single antenna radiator over which predefined system performance is achieved. The wireless communication system 102 provides wireless communication services to mobile units, such as mobile unit 144, which may be located in, or proximate to, one or more of the cells 114.
The wireless communication system 102 may be established within a structure, such as a building, or may be established in a combination of structures. For example, each cell 114, may correspond to a floor of a building. Alternatively, multiple cells, such as cells 114, 126 of Figure 5 may correspond to different areas of the same floor. It should be understood, however, that the wireless communication system 102 of the present invention is equally adapted for use outside of any structure, or for use both inside and outside of one or more structures.
The wireless communication system 102 includes one or more wireless fixed base (WFB) stations 110, which are also simply called "base stations" herein. Each base station 110, is connected to an RF switch 112, respectively. Each switch 112, represents any well known RF (radio frequency) multi-position switch, having RF isolation among its positions of 20 dB or better. Additionally, the switch should have a switching speed commensurate with the intra-slot or intra-frame rates in a TDMA/TDD system.
Each switch 112, is connected to one or more cell antenna units (CAU) 118, respectively. The number of cell antenna units 118, respectively connected to each switch 112, may vary from switch to switch, or may be the same for all switches 112, 124, as in Figure 5. In the embodiment shown in Figure 1, the switch 112, is connected to four cell antenna units 118. Four CAUÆs per base station are considered to be optimum from system performance and cost considerations.
The cell antenna units 118, serve the dual purpose of extended site coverage from a single base and spatial diversity for avoiding and/or overcoming multipath fading. This type of diversity is called macro diversity, to reflect the large relative spacing (compared to a wavelength) between or among the antenna units 118.
With regard to site coverage, the cell antenna units 118, are placed throughout the region of interest in order to insure complete radio coverage and to overcome multipath fading at certain remote terminal locations. Specifically, one antenna unit 118, is placed in each sub-cell 116, of the cell 114. By having a plurality of cell antenna units 118, it is possible to have less base stations 110, (otherwise, one base station and its associated interface and controller (e.g. 108 and 140) would be required for each sub-cell 116), thereby greatly simplifying system installation and use and minimizing system cost.
The cell antenna units 118, are connected to their respective base station 110, via preferably coaxial cables that are each less than or equal to approximately 200 feet in length. Each antenna unit 118, preferably includes an antenna and a duplexer. The duplexer, for TDD operation, used to overcome cable losses, preferably includes a pair of RF (radio frequency) switches, a power amplifier for transmission to the various mobiles 144, and a low noise amplifier for reception from the various mobiles 144. DC power for the amplifiers and the control signals for selecting transmit or receive are provided over the coaxial cable.
Maximum transmitter power from the antennas 118, is preferably limited to 100 mW, peak power. Transmitter power is controlled to minimize adjacent channel interference and to adapt to system coverage needs.
The switch 112, selectively connects its respective base station 110, to its respective antenna units 118. At any moment of time, each base station 110, is connected to one antenna unit 118, via the switch 112. For example, at any moment of time, base station 110 is connected to one antenna unit 118A via switch 112.
Each base station 110, is a time division multiple access (TDMA) and/or time division duplex (TDD) radio system. A TDMA/TDD system makes use of successive time slots to alternately transmit or receive information. Generally, these transmit and receive time slots are grouped together to define a frame. Each base station 110, includes a transceiver (transmitter/receiver combination) that is connected to its respective switch 112. Each base station 110, employs well known wireless communication techniques to exchange information with mobile units 144 via the antenna units 118. The transmitter and receiver of the base station are alternately connected to the switch and the selected cell antennas synchronously with the downlink and uplink portions of the frame. Downlink is a transmission from the base to a mobile. Uplink is a transmission from the mobile to the base. Digital modulation techniques such as M-ary FSK or M-ary PSK are preferred. All deployed base stations are synchronized with respect to their transmit and receive cycles for lowest intra-system interference.
This operation of the present invention is preferably implemented by a base station controller 140, that is contained in each of the base station 110, in combination with a mobile unit controller 146 that is contained in each mobile unit 144. These controllers 140, 146, as well as the operation of the present invention pertaining to macro diversity, is described in greater detail below.
As discussed above, each mobile unit 114 listens to transmissions from the antennas 118, and determines which is "best". The manner in which this determination is made shall now be discussed.
The determination of "best" antenna is based on a number of factors which are implementation dependent. For example, the "best" antenna determination can be based on a received signal strength indication(RSSI). Alternatively, the "best" antenna determination can be based on bit error rate (BER) (e.g., by determining the instantaneous error rate from the eye pattern fill-in, referred to as a pseudo-error count.) Or, the "best" antenna determination can be based on any combination of the above. A decision based upon both factors reduces the chances for making a bad antenna selection. Techniques for determining RSSI and BER are well known to persons skilled in the relevant art.
The base station 110, is connected to a private branch exchange (PBX) 104 via interface module 108. The interface module 108, converts the radio signals from the base station 110, into a standard telecommunication interface, such as tip-ring, or any proprietary interface as warranted. The structure and operation of the interface module 108, will be apparent to persons skilled in the relevant art. The interface module 108, may be integrated with the PBXÆs or the base station 110, or may be distinct from both.
The interface module 108, base station 110, switch 112, and antennas 118 represent a radio sub-system 101. Similarly, if Figure 5, the interface module 120, base station 122, switch 124, and antennas 130 represent another radio sub-system 103.
The operation of the base station 110 and the mobile units 144 as discussed herein is preferably implemented using a base station controller 140, contained in each base station 110, and a mobile unit controller 146 contained in each mobile unit 144. These controllers 140, 144 may represent hardware implemented state machines, or may alternatively represent processors operating in accordance with software, or may represent any combination of the above.
The PBX 104 connects the radio sub-system 101, to a telephone network 106 (which may include local and/or long distance networks). In this manner, mobile units 144 can communicate with fixed and/or mobile units located outside of the cells 114, via the telephone network 106. The structure and operation of the PBX 104 and the telephone network 106 will be apparent to persons skilled in the relevant art.
4. The First Embodiment of the Present Invention 4.1. Description off the First Embodiment
The first embodiment of the present invention employs the configuration shown in Figure 1 and described above. It also implements both micro and macro diversity to overcome multipath fading effects. In the first embodiment of the present invention, separate slots in the frame are provided for control and data information. Each control slot is dedicated to a specific antenna. The first embodiment of the present invention is best applied to single base station applications.
4.2. Structure of the Frame (Figure 2A)
According to a first embodiment of the present invention, data and control signals are transferred between the base station 110, and the mobile units 144 using TDMA (time division multiple access) frames such as that shown in Figure 2A. The first embodiment is adapted for use on a per cell basis.
The downlink portion 204 includes k downlink control slots 208 and n downlink data slots 210. The uplink portion 206 includes k uplink control slots 212 and n uplink data slots 214. k is equal to the number of antennas 118 connected to the switch 112. Thus, in the example embodiment of Figure 1, k is equal to four. n is equal to five in the example frame 202 shown in Figure 2A, although the value of n is implementation dependent.
Each downlink control slot 208 is associated with one of the antennas 118 connected to the switch 112. Similarly, each uplink control slot 212 is associated with one of the antennas 118 connected to the switch 112. The downlink control slot 208 and the uplink control slot 212 associated with a particular antenna occupy the same relative position in the frame 202. For example, if downlink control slot 208C is associated with antenna 118B, then uplink control slot 212C is also associated with antenna 118B.
The operation of the wireless communication system 102 according to the first embodiment of the present invention shall now be described with reference to a flowchart 221 in Figure 2B. Flowchart 221 depicts the operational steps that are performed to exchange data and control signals between the base station 110 and an active mobile unit, such as mobile unit 144, during a telephone call that has been previously established (the procedure for establishing telephone calls is discussed below with reference to Figure 2C). The operational steps depicted in Flowchart 221 represent the operation of the base station 110 and the active mobile unit 144 during the exchange of a single frame 202, called the "current" frame 202. The steps of Flowchart 221 are performed for each frame. Flowchart 221 begins with step 220, where control immediately passes to step 222.
In step 222, the base station 110 enables the transmission of control messages via the antennas 118A-118D in the downlink control slots 208 of the current frame 202. Specifically, the base station 110 commands the switch 112 to connect the base station 110 to the antenna 118A. Then, the base station 110, transmits a control message via antenna 118A in downlink control slot 208A (it is assumed that downlink control slot 208A is always associated with antenna 118A for illustrative purposes). Then, the base station 110 commands the switch 112 to connect the base station 110 to the antenna 118B.
Then, the base station 110 transmits a control message via antenna 118B in downlink control slot 208B (it is assumed that downlink control slot 208B is always associated with antenna 118B for illustrative purposes). Similarly, the base station 110 transmits the same control messages via antennas 118C and 118D in downlink control slots 208C and 208D, respectively (it is assumed that downlink control slots 208C and 208D are respectively, always associated with antennas 118C and 118D for illustrative purposes). In this way, the base station, 110, broadcasts the same message through each of its associated antennas, 118.
Note that steps 222 and 224 (just described) were performed by the base station 110. Steps 226, 228, 230, and 232 are performed by each active mobile unit. For illustrative purposes, these steps are described with respect to mobile unit 144.
It is noted that the mobile unit 144 previously synchronized to, and maintains synchronization with, the timing of the frames transmitted from the base station 110 in any well known manner.
In step 228, the mobile unit 144 receives data in the downlink data slot 210 assigned to it. As discussed above, for the current frame, each active mobile unit is associated with a downlink data slot 210. This association may change from frame to frame (see step 226, described above). During step 228, the mobile unit 144 receives data in the downlink data slot 210 previously assigned to it.
In step 230, the mobile unit 144 transmits, if necessary, a request for a new antenna to the base station 110 in the uplink control slot 212 associated with its currently assigned antenna. This is a random process in time. The mobile decides when it needs improved performance as a function of time and its position at that time. For example, suppose that the mobile unit 144 is currently assigned to antenna 118A. Also suppose that in step 226 the mobile unit 144 determined that antenna 118C was the best antenna for its purposes. Accordingly, in step 230, the mobile unit 144 transmits a request for a new antenna (i.e., antenna 118C) to the base station 110 in the uplink control slot associated with the new best antenna 118C. Preferably, the mobile unit 144 only transmits such a request if the "best" antenna (determined in step 226) differs from its currently assigned antenna. Note that any request for a new antenna does not affect the operation of the mobile unit 144 during the current frame 202.
A poling procedure can also be used instead of the random access procedure just described. Each mobile is periodically queried to determine its state or need for service. For example, each mobile is asked to respond to the base via the best antenna at a particular time until all mobiles have been poled. During this response, requests for call establishment can be made. In a small system, e.g., less than 12 mobiles, the delay time for a response (with a 10 ms. frame duration) is less than or equal to 120 ms. Inactive mobiles do not have to be poled continuously, as long as the poling rate is short enough to provide acceptable dial tone delay. Poling insures that a contemplated action is acknowledged before an action is taken.
In either the random or poled case, however, the need for a change request from the mobile is required before any change proceeds.
In step 232, the mobile unit 144 transmits data to the base station 110 in the uplink data slot 214 assigned to the antenna that it is currently monitoring. As discussed above, for the current frame, each active mobile unit is associated with an uplink data slot 214. This association may change from frame to frame and from call to call(reference is made to step 226, described above). During step 232, the mobile unit 144 transmits data in the uplink data slot 212 previously assigned to it. The base station 110 transfers this data to the telephone network 106 via the interface module 108 and the PBX in a well known manner. After performing step 232, performance of flowchart 221 is complete as indicated by step 234.
The operation of the wireless communication system 102 according to the first embodiment of the present invention shall now be further described with reference to a flowchart 240 in Figure 2C. Flowchart 240 depicts the operational steps that are performed to establish a new telephone call between a mobile unit, such as mobile unit 144, and a base station, such as base station 110. The steps of Flowchart 240 are performed each time a mobile unit 144 attempts to establish a new telephone call. Flowchart 240 begins with step 242, where control immediately passes to step 244.
In step 244, a mobile unit, such as mobile unit 144, wishing to establish a new telephone call listens to all of the downlink control slots 208 in the current frame 202 (that is, the mobile unit 144 attempts to receive the control messages contained in all of the control slots 208). The mobile unit 144 determines which of the antennas 118A-118D is the "best" antenna. Procedures for determining the "best" antenna are discussed above. It is noted that the mobile unit 144 previously synchronized to, and maintains synchronization with, the timing of the frames transmitted from the base station 110 in any well known manner.
In accordance with the random or poled access procedures, in step 246, the mobile unit 144 transmits a request to establish a new telephone call to the base station 110 in the uplink control slot 212A associated with the "best" antenna 118A.
The request to establish a new telephone call may not be clearly transmitted to the base station 110. This may be due to noise or other effects in the communication environment. This may also be due to conflict between multiple mobile units attempting to transmit during the same uplink control slot 212 (for example, it is possible that two or more mobile units may transmit during the same control slot, having made similar decisions about the best antenna). The unsuccessful transmission of a new telephone call request does not adversely affect the operation of the system, since the mobile unit 144 can resend the request (if necessary) in the next frame. In addition, there are well known colloision algorithms that can be employed to mitigate these conflicts.
Upon receiving the request for a new telephone call from the mobile unit 144, the base station 110 determines whether to accept the request. The base station 110 makes this determination as follows: If the base station 110, has less than n (the # of downlink data slots) active mobiles to which it is transmitting data in active slots, then any one of the unused data slots is assigned to the mobile and the call is accepted.
In the case presented here, the mobile unit can choose an unused uplink control slot to transmit on at a random time (as opposed to when requested to by the base.) Such transmissions are termed random access here. Random access transmissions would be used to initiate communication with the base for the purpose of setting up a voice call, for example.
In step 248, the mobile unit 144 reads control information, if any, contained in the downlink control slot 208 associated with the "best" antenna (determined in step 244) of the next frame. As just discussed above, if the base station 110 accepted the request for a new telephone call, then the base station 110 would have communicated that acceptance in this downlink control slot 208. If this downlink control slot contains an acknowledgment of the mobileÆs request (step 249) from base station 110, but does not contain a call acceptance flag (step 250), then the mobile unit 144 determines that the call request was not accepted (step 250), and returns to step 244. On the other hand, if the mobile does not receive an error free response from the base station, the mobile unit assumes the request was not received error-free and retransmits in accordance with step 246. To avoid an endless loop condition, the mobile unit can cease the request after m tries.
If the new call request was accepted (as determined in step 250), then the mobile unit 144 in step 252 makes any adjustments that are necessary to prepare for the immediately following frame (this "immediately following frame" is the frame which follows the "next frame"; recall that the "next frame" followed the "current frame), such as adjusting for the frequency and the data slots assigned to the mobile unit 144 (see step 248). Operation of the flowchart 240 is complete after the completion of step 252, as indicated by step 254. Once the call is established, operation of the base station 110 and the mobile unit 144 is as shown in Figure 2B, described above.
According to a second embodiment of the present invention, data and control signals are transferred between the base station 110, and the mobile units 144 using TDMA (time division multiple access) frames such as that shown in Figure 3A. The physical structure of the second embodiment of the present invention is the same as that shown in Figure 1 and described in Section 2, above. The second embodiment differs from the first embodiment in that the control and data information are now combined into specific fields of one slot. The number of these combined function slots in a frame is implementation dependent, but there is always one slot for each active call or other activity in the system. The second embodiment also employs both macro and micro diversity.
The downlink portion 304 includes x downlink, combined control/data slots 308 and are herein after referred to simply as slots. The uplink portion 306 includes x uplink slots 312. The quantity x is equal to 8 in the example frame 302 shown in Figure 3A, although the value of x is implementation dependent.
Figure 4 illustrates the format of the downlink and uplink slots 308, 312. Each downlink and uplink slot 308, 312 includes a control field 402 and a single data field 404. The control field is broken down further into several sub-fields, as shown in Figure 4. For example, the field 402E might contain control information such as guard bits, preamble bits, synchronization bits and check bits. Finally, subfield 402F might contain system messages associated with usable frequencies, usable uplink slots, terminal status, update control messages and check bits. The fields 402A through D are referred to as z fields. Their number is equal to the number of antennas 118 connected to the switch 112 (thus, z is equal to 4, in this example). Each z field 402A-D, is associated with one of the antennas 118 connected to the switch 112. The z fields are pertinent to the present invention. Their specific location is not important as long as they are present and their fixed position is known so that they can be monitored.
The size of the z fields is at least two bits. Longer bit streams can be used and the patterns of the bits can be chosen to meet performance and cost goals of the system. The longer the pattern, in general, the more robust the detection of it, but the greater the cost for the circuitry/algorithms involved. The mobile can make a decision based upon the RSSI in each z field, or the number of errors in each z field, or both.
The foregoing description of the makeup of the control field 402, is meant to illustrate the kinds of information that a knowledgeable system designer might place in such fields.
The operation of the wireless communication system 102 according to the second embodiment of the present invention shall now be described with reference to flowchart 320 in Figure 3B. Flowchart 320 depicts the operational steps that are performed to exchange data and control signals between the base station 110 and an active mobile unit, such as mobile unit 144, during a telephone call that has been previously established (the procedure for establishing telephone calls according to the second embodiment is discussed below with reference to Figure 3C). The operational steps depicted in Flowchart 320 represent the operation of the base station 110 and the active mobile unit 144 during the exchange of a single frame 302, called the "current" frame 302. The steps of Flowchart 320 are performed for each frame. Flowchart 320 begins with step 322, where control immediately passes to step 324.
Assume that the active call from Mobile unit 144, is associated with the downlink slot 308A and uplink slot 312A. In step 324, the base station 110 enables the transmission of the control field 402 of the downlink slot 308A of the current frame 302 via the antennas 118A-118D in the following manner. For illustrative purposes assume that the antenna 118A is assigned to the mobile unit 144 during the current frame 302. For the purposes of transmitting System Related Fields 402E and System Messages 402F, the base station 110 commands the switch 112 to connect the base station 110 to the antenna 118A. For the purposes of transmitting the z-fields associated with each antenna, the base station 110 commands the switch 112 to connect the base station 110 to the antenna assigned to a z-field during that z-field's portion of the slot. For example, if z-field 402B was assigned to antenna 118B then the base station 110 commands the switch 112 to connect the base station 110 to antenna 118B during z-field 402B.
In step 326, the base station 110 enables the transmission of a data message intended for mobile unit 144 via the antenna unit associated with the mobile unit (118A). This data message was received from the telephone network 106 via the PBX 104 and the interface module 108. This data message is transmitted in data field 404 of downlink slot 308A of the current frame 302. In step 326, the base station 110 commands the switch 112 to connect base station 110 to antenna 118A during the transmission of data field 404 of downlink slot 302A of the current frame 302.
In step 332, the mobile unit 144 listens to its assigned downlink slot 308A including all contained control and data fields. From the reception of the z-fields, the mobile unit 144 determines which of the antennas 118A-118D is the "best" antenna. Procedures for determining the "best" antenna are discussed above. Also during step 330, the mobile unit extracts system information inserted into the system message field 402F of downlink slot 308A by the base station 110 during step 324 (described above). Such information may affect the operation of the base station and mobile unit 144 during the next frame (that is, the frame that immediately follows the current frame) as described above.
Upon noting a change in the z fields from the mobile unit 144, the base station 110 determines which antenna to use for that mobile in the next downlink frame. The manner in which the base station 110 makes this determination is described above.
In step 336, the mobile unit 144 transmits data to the base station 110 in the data field 404 of its uplink slot 312A in the current frame. The base station 110 transfers this data to the telephone network 106 via the interface module 108 and the PBX in a well known manner. After performing step 336, performance of flowchart 320 is complete as indicated by step 338.
The operation of the wireless communication system 102 according to the second embodiment of the present invention shall now be further described with reference to a flowchart 340 in Figure 3C. Flowchart 340 depicts the operational steps that are performed to establish a new telephone call between a mobile unit, such as mobile unit 144, and a base station, such as base station 110, according to the second embodiment. The steps of Flowchart 340 are performed each time a mobile unit 144 attempts to establish a new telephone call. Flowchart 340 begins with step 342, where control immediately passes to step 344.
The base station 110, is required to transmit system information in at least one downlink slot of every frame. To aid in clearly describing the process, assume that this required slot is slot 308E, for example. In step 344, a mobile unit, such as mobile unit 144, wishing to establish a new telephone call, synchronizes to a downlink slot (such as downlink slot 308E) in the current frame 302. The mobile unit 144 recognizes from its contents, that slot 308E is a general purpose, informational slot transmitted by the system. Slots of this type are called beacon slots.
A beacon slot contains control information of the type described above in the discussion of the control fields 402. A beacon slot does not necessarily have an information field associated with it, but it could have one, if the traffic load demands it. In that sense, for this embodiment of the present invention, any active slot can be considered to be a beacon slot for the system. For example, slot 308E could be a beacon slot containing system information such as the base stationÆs good frequency list at that moment and the slots available for new calls in the next frame or mobile responses in the uplink of the current frame. The base station continuously monitors all uplink slots in every frame. The Mobile unit 144, wanting service, syncs to beacon slot 308E and reads the system information.
In step 348, the Mobile unit 144, compares its own good frequency list to the base station list and selects a mutually acceptable frequency. There may be a delay involved if the chosen frequency is low on a list of sequentially used frequencies acceptable to the base station, since the base station may take several frames per frequency to pass through its entire list. From the available uplink slots, the Mobile 144, also selects its uplink slot. For example, the chosen slot could be slot 312E.
If the new call request was accepted (as determined in step 352), then the mobile unit 144 in step 356 transmits data in its assigned uplink slot 312. Operation of the flowchart 340 is complete after the completion of step 356, as indicated by step 358. Once the call is established, operation of the base station 110 and the mobile unit 144 is as shown in Figure 3B, described above.
Since the base is not aware of when or on what slot mobile units will initiate a dialogue, the random access mode of communication requires that the antennas associated with the base be connected simultaneously for the period of time associated with each of the unassigned uplink slots. This mode of operation of the CAU switch 112, is termed BIG EAR, since all CAUs connected to the base station via the switch 112, are listening at the same time. In this way, the WFB 110, will be able to receive the mobile unitÆs uplink transmission without having to know where the mobile unit is. Once having received the initial transmission, the WFB 110, would utilize the assigned antenna for its transmitted response back to the mobile, acknowledging assignment of the chosen slot for communication with the mobile unit, as described above. Until indicated otherwise, the assigned antenna would be used by the WFB 110, for both reception and transmission of the assigned slot, unless one of the z fields changes as described above.
6. Third Embodiment - Use in Multi-Cell Systems
The frame structure described for the second embodiment of the invention (without antenna control) has been used by other wireless systems in the past (e.g., Digital European Cordless Telecommunication (DECT) system) to span many cells. With reference to Figure 5, the operation of these and like systems allows for the user data service to be provided on an uninterrupted basis as an active mobile unit is moved from one cell to the next, e.g., from cell 114 to cell 126. Such a capability, known as hand-off, is made possible through hardware additions and control protocol additions to the single cell system described above. Such additions are well known to system designers and persons skilled in the art of wireless systems. For example, a feature of the PBX 104, needs to be added to provide for connectivity changes from one WFB 110, to a second WFB 122, during a voice conversation. In addition, certain control codes must be added to the control fields in both the stationary end (WFBs 110,122, Interface/controller 108,140 and 120,142, or PBX 104) and mobile unit 144, and its controller 146, to accomplish the tasks and communication necessary for hand-off.
Hand-off is a process which, because of its high impact on shared hardware and control resource utilization, should be used sparingly. This is allowed for by choosing hand-off criteria that allow for switching between cells only when the general performance of one cell has degraded to the extent that hand-off to another cell (if better) is warranted. In general, this results in two characteristics we wish to discuss further: 1) the number of hand-offs during the time a mobile unit is active (e.g., on a call) is on the order of one or two per minute; and 2), the time over which the transition occurs (from recognition that hand-off is needed to completion of hand-off) occurs over many frames (e.g., 40 to 50).
Thus, the metrics used to determine when hand-off is needed are those that tend not to include the short term variations in signal quality which the present invention is able to combat. For example, the invention might use measures of BER variations over two frames to determine best antenna for a subsequent frame and subsequently, antenna switching can occur on every frame. On the other hand, hand-off criteria are averaged over many frames (20 to 30) and the interval between hand-offs would occur on the order of seconds to minutes. The operation of the present invention serves to provide better service within a cell by combating short term impairment occurrences. Hand-off, on the other hand, combats long term impairments due to inter-cell movement. In this way, the operation of the present invention does not hinder the operation necessary for inter-cell hand-off, and, in fact, uses it for multi cell operation, as well.
A method of achieving increased coverage and macro diversity from a single base station in a wireless communication system having a base station coupled to N antennas, comprising the steps of:
(1) transmitting from said base station N control messages each via one of said antennas;
(2) transmitting a data message addressed to a mobile unit via a particular one of said antennas previously assigned to said mobile unit for the duration of an active call;
(3) receiving in said mobile unit said control messages and said data message;
(4) analyzing in said mobile unit said control messages to identify from said antennas a best antenna;
(5) transmitting from said mobile unit to said base station a new antenna request identifying said best antenna in an uplink control slot of a frame, said uplink control slot being associated with said particular one of said antennas; and
(6) using in response to said new antenna request said best antenna to transmit from said base station one or more subsequent data messages addressed to said mobile unit.
The method of claim 1, wherein step (1) comprises the steps of:
(a) connecting said base station to one of said antennas;
(b) transmitting from said base station a control message via said one of said antennas in a downlink control slot of said frame, said downlink control slot being associated with said one of said antennas;
performing steps (a) and (b) for each of said antennas.
The method of claim 1, wherein step (2) comprises the step of: transmitting said data message via said particular one of said antennas in a downlink data slot previously assigned to said mobile unit.
The method of claim 1, further comprising the following steps which are performed after step (4):
determining whether said best antenna is equal to said particular one of said antennas previously assigned to said mobile unit; and
bypassing performance of step (5) if said best antenna is equal to said particular one of said antennas previously assigned to said mobile unit.
(7) receiving in a second mobile unit desiring to establish a new telephone call said control messages;
(8) analyzing in said second mobile unit said control messages to identify from said antennas a best antenna with respect to said second mobile unit; and
(9) transmitting from said second mobile unit to said base station a new telephone call request identifying said best antenna with respect to said second mobile unit in a second uplink control slot of said frame, (said second uplink control slot being associated with said best antenna with respect to said second mobile unit.)
(1) transmitting from said base station N control messages in N control fields of a downlink control/data slot of a frame, said downlink control/data slot being associated with a mobile unit for the duration of an active call, each of said control messages being transmitted via one of said antennas;
(2) transmitting a data message addressed to said mobile unit in a data field of said downlink control/data slot, said data message being transmitted via a particular one of said antennas previously assigned to said mobile unit;
(5) transmitting from said mobile unit to said base station a new antenna request identifying said best antenna in a control field of an uplink control/data slot of said frame, said uplink control/data slot being associated with said mobile unit for the duration of an active call, said control field of said uplink control/data slot being associated with said particular one of said antennas; and
The method of claim 6, wherein step (1) comprises the steps of:
(b) transmitting from said base station a control message via said one of said antennas in one of said control fields, of said downlink control/data slot, associated with said one of said antennas;
The method of claim 6, further comprising the following steps which are performed after step (4):
The method of claim 6, further comprising the steps of: (7) transmitting from said base station control messages in control fields of a downlink slot, called a beacon slot, of said frame, (each of said control messages including information identifying slots and frequencies available for use in new telephone calls; and including information transmitted from each antenna in turn) <---Needs work!
(8) receiving in a second mobile unit desiring to establish a new telephone call said beacon control messages;
(9) analyzing in said second mobile unit said control messages to identify from said antennas a best antenna with respect to said second mobile unit;
(10) selecting one of said available slots;
(11) transmitting from said second mobile unit to said base station a new telephone call request identifying said selected available slot and said best antenna with respect to said second mobile unit in a control field of an uplink slot of said frame;
A radio sub-system of a wireless communication system, comprising:
N antennas each positioned in a sub-cell of a cell;
a switch connected to said base station and to said antennas, to selectively connect said base station to said antennas; and
means for transmitting N control messages each via one of said antennas; and
means for transmitting a data message addressed to said mobile unit via a particular one of said antennas previously assigned to said mobile unit; said mobile unit comprising:
means for receiving said control messages and said data message;
means for analyzing said control messages to identify from said antennas a best antenna; and
means for transmitting to said base station a new antenna request identifying said best antenna.
The radio sub-system of claim 10, wherein said base station further comprises:
means for using in response to said new antenna request said best antenna to transmit one or more subsequent data messages addressed to said mobile unit.
The radio sub-system of claim 10, further comprising a second mobile unit desiring to establish a new telephone call, said second mobile unit comprising:
means for receiving said control messages;
means for analyzing said control messages to identify from said antennas a best antenna with respect to said second mobile unit; and
means for transmitting to said base station a new telephone call request identifying said best antenna with respect to said second mobile unit.
means for transmitting N pilot control messages in N control fields of a downlink beacon slot, each of said beacon control messages including information identifying (frequency-time) slots available for use in new telephone calls.
The radio sub-system of claim 13, further comprising a second mobile unit desiring to establish a new telephone call, said second mobile unit comprising:
means for receiving said beacon control messages;
means for analyzing said beacon control messages to identify from said antennas a best antenna with respect to said second mobile unit;
means for selecting one of said available time slots and frequency channels;
means for transmitting to said base station a new telephone call request identifying said selected available slot and said best antenna with respect to said second mobile unit in a control slot of an uplink slot.
EP19950306066 1994-09-12 1995-08-30 Wireless communication system using distributed switched antennas Expired - Lifetime EP0702462B1 (en)
US08/304,319 US5628052A (en) 1994-09-12 1994-09-12 Wireless communication system using distributed switched antennas
US304319 2002-11-25
EP0702462A1 true EP0702462A1 (en) 1996-03-20
EP0702462B1 EP0702462B1 (en) 2002-10-16
ID=23176015
EP19950306066 Expired - Lifetime EP0702462B1 (en) 1994-09-12 1995-08-30 Wireless communication system using distributed switched antennas
US (1) US5628052A (en)
EP (1) EP0702462B1 (en)
JP (1) JPH0888599A (en)
CA (1) CA2154303C (en)
DE (2) DE69528561D1 (en)
GB2318482A (en) * 1996-10-16 1998-04-22 Ico Services Ltd Channel selection in a radio communication system employing diversity
WO1998038824A1 (en) * 1997-02-27 1998-09-03 Nokia Telecommunications Oy Method of implementing a handover in a cellular radio system
WO1998038825A1 (en) * 1997-02-27 1998-09-03 Nokia Telecommunications Oy Method of implementing dynamic channel allocation in a cellular radio system
WO1998054850A2 (en) * 1997-05-30 1998-12-03 Silicon Wireless Limited Method and apparatus for wireless communication employing control for confidence metric bandwidth reduction
WO1999039456A1 (en) * 1998-02-02 1999-08-05 Silicon Wireless Limited Method and apparatus for collector arrays of directional antennas co-located with zone managers in wireless communications systems
WO1999039455A1 (en) * 1998-02-02 1999-08-05 Silicon Wireless Limited Method and apparatus for collector arrays in wireless communications systems
EP0969610A2 (en) * 1998-07-02 2000-01-05 Lucent Technologies Inc. Code division multiple access communication with enhanced multipath diversity
WO2001015336A1 (en) * 1999-08-25 2001-03-01 Mdiversity, Inc. Method and apparatus for wireless communication employing control for broadcast transmission
EP1211820A1 (en) * 2000-12-01 2002-06-05 Lucent Technologies Inc. Method for simultaneously conveying information to multiple mobiles over multiple antennas
EP1566897A2 (en) * 1995-04-28 2005-08-24 Nec Corporation A mobile station in a transmission diversity system and respective method
EP1908002A2 (en) * 2005-06-10 2008-04-09 Mckesson Automation Inc. Inventory management system using rfid tags to aid in dispensing and restocking inventory
GB2466708A (en) * 2008-12-31 2010-07-07 Motorola Inc A MIMO transmitter adapts power allocation to antennas depending on whether the transmission is non-MIMO, MIMO rank-1 or MIMO-rank-2
WO2018055179A1 (en) * 2016-09-26 2018-03-29 Safran Electronics & Defense Method for selecting an antenna
CN1918800B (en) * 2004-02-13 2010-08-25 夏普株式会社 Transmitter, receiver, communication device, radio communication system, data transmitting method and data receiving method
KR101659090B1 (en) * 2010-04-04 2016-09-23 엘지전자 주식회사 Method and apparatus for transmitting data of user equipment in distributed antenna system
CN102244943B (en) * 2011-07-25 2013-08-28 成都芯通科技股份有限公司 Low-noise-amplifier bypass system in multi-carrier base station amplifier and control method thereof
1994-09-12 US US08/304,319 patent/US5628052A/en not_active Expired - Lifetime
1995-07-20 CA CA 2154303 patent/CA2154303C/en not_active Expired - Fee Related
1995-08-30 DE DE1995628561 patent/DE69528561D1/en not_active Expired - Lifetime
1995-08-30 EP EP19950306066 patent/EP0702462B1/en not_active Expired - Lifetime
1995-08-30 DE DE1995628561 patent/DE69528561T2/en not_active Expired - Lifetime
1995-09-12 JP JP7258216A patent/JPH0888599A/en active Pending
PATENT ABSTRACTS OF JAPAN vol. 013, no. 298 (E - 784) 10 July 1989 (1989-07-10) *
EP1566897A3 (en) * 1995-04-28 2006-04-12 Nec Corporation A mobile station in a transmission diversity system and respective method
AU732544B2 (en) * 1997-02-27 2001-04-26 Nokia Telecommunications Oy Method of implementing a handover in a cellular radio system
WO1998054850A3 (en) * 1997-05-30 1999-05-14 Silicon Wireless Limited Method and apparatus for wireless communication employing control for confidence metric bandwidth reduction
EP0969610A3 (en) * 1998-07-02 2004-06-16 Lucent Technologies Inc. Code division multiple access communication with enhanced multipath diversity
US5628052A (en) 1997-05-06
CA2154303C (en) 1999-12-07
EP0702462B1 (en) 2002-10-16
DE69528561D1 (en) 2002-11-21
CA2154303A1 (en) 1996-03-13
JPH0888599A (en) 1996-04-02
DE69528561T2 (en) 2003-06-26
Ref document number: 69528561