Primary station for efficiently covering a sectorized cell utilizing beam forming and sweeping

Description of equivalent WO 2004004148 A1

[0001] SYSTEM FOR EFFICIENTLY COVERING A SECTORIZED

CELL UTILIZING BEAM FORMING AND SWEEPING

[0002] BACKGROUND

[0003] Sectoring is a well known technique for providing distinct coverage area from individual cell sites and can be achieved with "smart antenna" technology, which is well known in the art. Smart antenna methods dynamically change the radiation pattern of an antenna to form a "beam," which focuses the antenna's topographical coverage.

[0004] Beam forming is an enhancement on sectoring in that the sectors can be adjusted in direction and width. Both techniques are employed to: 1) reduce interference between cells and the user equipment (UE) deployed within the cells; 2) increase the range between a receiver and a transmitter; and 3) locate a UE. These techniques are usually applied to the dedicated channels of the UEs once their general location is known. [0005] Prior to knowing the location of a UE, the common channels broadcast information that all UEs may receive. While this information may be sent in static sectors, it is not sent in variable beams. There are inherent inefficiencies in this approach in that extra steps are required to determine the appropriate beam to use for the dedicated data exchanges. Additionally, the beam^'s must be generally large enough to provide a broad coverage area, which in turn means their power with distance from the transmitter is lower. In such cases, they must use higher power, have longer symbol times and/or more robust encoding schemes to cover the same range.

[0006] Common channel coverage using a prior art scheme is shown in

Figure 1 as four overlapping wide beams. This provides omni-directional coverage, while giving a degree of reuse to the cell site. It also provides a coarse degree of directivity to the UEs (UE1, UE2) detecting one of the transmissions, by having each sector transmit a unique identifier. [0007] Referring to Figure 2, downlink dedicated beams between a primary station (P) and several UEs (UE3, UE4) are shown. Assuming the same power from the primary station (P) for Figures 1 and 2 and all other attributes being equal, the UEs (UE3 and UE4) shown in Figure 2 can be further away from the primary station P than the UEs (UEl, UE2) shown in Figure 1. Alternatively, the coverage areas can be made approximately the same by decreasing the symbol rate and/or increasing the error correction coding. Either of these approaches decreases the data delivery rate. This also applies to the receiver uplink beam patterns of the primary station P; and the same comments about coverage and options apply for data from the UEs to the primary station P.

[0008] In the prior art, the range of a primary station P or a UE is generally increased by combinations of higher power, lower symbol rates, error correction coding and diversity in time, frequency or space. However, these methods yield results that fall short of optimized operation. Additionally, there is a mismatch between the common and dedicated communications channels in the ways that coverage is aligned. [0009] There exists a need for efficiently covering a sectorized cell without the drawbacks associated with prior art schemes.

[0010] SUMMARY

[0011] A communication system for transmitting and receiving communications between at least one primary station and at least one secondary station in a sectorized cell using at least one beam comprising an antenna. The system includes a device for generating and shaping the beam; and a device for sweeping the shaped beam. The sweeping device selectively directs the shaped beam at a plurality of directions.

[0012] BRIEF DESCRIPTION OF THE DRAWING(S)

[0013] Figure 1 is a prior art common channel coverage scheme between a primary station and several UEs with four overlapping wide beams.

[0014] Figure 2 is a prior art scheme of downlink dedicated beams between a primary station and several UEs using dedicated beams.

[0015] Figure 3 is a rotating common channel beam emanating from a primary station. [0016] Figure 4 is a beam configuration for known uneven distribution of UEs.

[0017] Figure 5 is a beam configuration having beam width adjusted for traffic type.

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0019] The present invention will be described with reference to the drawing figures where like numerals represent like elements throughout. The foregoing statements about beam forming are applicable to both transmission of the signal and its reception. For example, narrower transmission beams cause less interference to those devices outside the beam. Conversely, a narrower reception beam decreases interference from signals outside the beam. The foregoing description of the invention is applicable to both the reception and transmission of signals. The context of a particular part of the description will sometimes explicitly refer to reception or transmission when this is not case.

[0020] The common channels are utilized, as their name implies, by all devices. The system and method of the present invention formats these common channels in a fashion that provides useful information to the system and the UE for eventual establishment of the dedicated channels. [0021] Referring to Figure 3, the dashed outlines represent possible positions Pι-P_n for a common channel beam B emanating from a primary station (PS). At a particular time period, the beam B exists only in one of the positions Pi as illustrated by the solid outline. The arrow shows the time sequencing of the beam B. In this illustration, the beam B sequentially moves from one clockwise position Pi to another P2-P-1, although a clockwise rotation is not necessary.

[0022] The system provides for identifying the beam B at each of the positions Pι-P . A first embodiment for identifying the beam B is to send a unique identifier while the beam B is at in each position Pι-P_n. For example, at a first position Pi a first identifier Ii will be transmitted, at a second position P₂ a second identifier I2 will be generated, and so on for each of the positions Pi-Pn. If the beam B is swept continuously, a different identifier Ii- Im may be generated for each degree, (or preset number of degrees), of rotation.

[0023] A second embodiment for identifying the position Pι-P_n of the beam B is to use a time mark as a type of identifier, which the UE returns to the PS. Returning either the time mark (or the identifier) to the PS informs the PS which beam B was detected by the UE. For that time period, the PS now knows the position Pι-P_n of the beam B that was able to communicate with the UE. However, it should be noted that due to possible reflections, this is not necessarily the direction of the UE from the PS.

[0024] A third embodiment for identifying the position Pι-P_n of the beam

B is to use time-synchronization. The beam B is positioned and correlated with a known time mark. One way of achieving this would be for both the UEs and the PS to have access to the same time reference, such as the global positioning system (GPS), National Institute of Standards and Technology internet time or radio time broadcasts (WWV) or local clocks with adequate synchronization maintained.

[0025] A fourth embodiment for identifying the position Pι-P_n of the beam B is for the UEs and the PS to synchronize to timing marks coming from the infrastructure transmissions. The UEs can detect beam transmissions identifying the PS, but not necessarily the individual beam B positions Pι-P_n. By the UE reporting back to the PS the time factor when it detected the beam B, the PS can determine which beam B the UE is referencing. The benefit of this embodiment is that the common channel transmission does not have to be burdened with extra data to identify the position Pι-P_n of the beam B. [0026] A fifth embodiment for identifying the position of the beam B is to incorporate a GPS receiver within the UE. The UE can then determine its geographical location by latitude and longitude and report this information to the PS. The PS can then use this information to precisely generate the direction of the beam B, beam width and power. Another advantage of this embodiment is the precise location obtained of the UE, which will allow users to locate the UE if the need arises. [0027] Referring to Figure 4, the location pattern may be tailored as desired by the system administrator. In this manner, the PS may position the beam B in a pattern consistent with the expected density of UEs in a particular area. For example, a wide beam Wi, W2, W3 may be cast in positions Pi, P2, P3, respectively, with few UEs, and more narrow beams N4, N5, NΘ cast in positions P₄, P5, Pβ, respectively, with many UEs. This facilitates the creation of narrower dedicated beams B in the denser areas, and also increases the capacity for the uplink and downlink use of the common channels to establish initial communications.

[0028] The beam width manipulation is preferably performed in real time. However, the conditions of communication and the nature of the application determine the suitability of number of beam positions Pι-P and their associated beam width patterns. The beam patterns formed should be sufficiently wide such that the number of UEs entering and leaving the beam can be handled without excessive handoff to other beams. A static device can be serviced by a narrow beam. Swiftly moving cars for example, could not be serviced effectively by a narrow beam perpendicular to the flow of traffic, but could be serviced by a narrow beam parallel to the direction of travel. A narrow perpendicular beam would only be adequate for short message services, not for voice services, such as phone calls.

[0029] Another advantage to using different beam widths is the nature of the movement of UEs within a region. Referring to Figure 5, a building BL is shown (representing an area having primarily slower moving pedestrian- speed devices UE_S), and a highway H is shown (representing an area having primarily faster-moving devices UEf). The slower speed devices UE_S can be served by narrow beams N1-N3 that are likely to be traversed during a communication time period. Alternatively, the faster moving devices UEf require wider beams W1-W3 to support a communication. [0030] Beam width shaping also decreases the frequency of handover of

UEs from one beam B to another. Handover requires the use of more system resources than a typical communication since two independent communication links are maintained while the handover is occurring. Handover of beams also should be avoided because voice communications are less able to tolerate the latency period often associated with handover.

[0031] Data services are packet size and volume dependent. Although a few small packets may be transmitted without problems, a large packet requiring a significant number of handovers may utilize excessive bandwidth. This would occur when links are attempted to be reestablished after a handover. Bandwidth would also be used up when multiple transmissions of the same data is sent in an attempt to perform a reliable transfer. [0032] Downlink common channel communication will often be followed by uplink transmissions. By knowing the transmission pattern of the PS, the UE can determine the appropriate time to send its uplink transmission. To perform the necessary timing, a known fixed or broadcast time relationship is utilized. In the case of a fixed relationship, the UE uses a common timing clock. The UE waits until a predetermined time in which the PS has formed a beam over the UE's sector before transmitting. In the case of a broadcast, the PS informs the UE when to send its uplink signal. The uplink and downlink beam forming may or may not overlap. It is often an advantage to avoid overlap, so that a device responding to a transmission can respond in less time than would be required to wait an entire antenna beam forming timing cycle for the same time slot to occur.

[0033] It should be noted that CMDA and other RF protocols utilize some form of time division. When responding to these types of temporal infrastructures, both beam sectoring and the time slots of the protocol would be of concern. Other non-time dependent RF protocols, such as slotted Aloha would only involve sectoring.

[0034] The embodiment described hereinbefore was directed to

"sweeping" the beam B around a PS in a sequential manner. In many instances this will typically be the most convenient way to implement the invention. There are, however, alternative ways to assume the various positions. For instance, it may be desirable to have more instances of coverage in certain areas. This could be done generating the beam in a sequence of timed positions. For instance, if there are 7 positions, (numbered 1 through 7), a sequence of (1, 2, 3, 4, 2, 5, 6, 2, 7, 1) could be used. This would have the area covered by beam position number 2 more often than other positions, but with the same dwell time. It might also be desirable to have a longer dwell time in a region. The sequence (1, 2, 3, 4, 4, 5, 6, 7, 1) for instance would have beam position number 4 remain constant for two time periods. Any suitable sequencing could be utilized and modified as analysis of the situation warranted.

[0035] Likewise, it is not necessary to restrict the beam positions to a rotating pattern. The beam positions could be generated in any sequence that serves the operation of the communication system. For example, a pattern that distributed the beams B over time such that each quadrant was covered by at least one beam B might be useful for UEs that are closer to the PS and are likely to be covered by more than one beam position.

[0036] It should be noted that similar to all RF transmissions, an RF signal only stops at a physical point if there is a Faraday-type of obstruction, (e.g. grounded metal roof). Usually the signal dies off, and the boundary is some defined attenuation value from the peak value of the transmission. To provide adequate coverage in the application of this invention, it is preferable that adjacent beam positions overlap to some degree. The overlap will tend to be more pronounced closer to the transmission and reception antennas. Close to an infrastructure antenna site, any UE is therefore likely able to communicate via a number of differently positioned beams B. Devices able to communicate via several beam positions could therefore, if needed, achieve higher data rates using these multiple positions. Devices further away, however, are more likely to be able to communicate via only once instant of beaming, and to obtain higher data rates would require another technique such as a longer dwell time.