GB2508864A - Pilot signal power control in a wireless communication system - Google Patents

Abstract

An access point (104) for a cellular communication system is arranged to control the transmit power of its pilot signal by switching the pilot signal periodically between an "on" state and an "off" state with configurable "on" and "off' times. The "on" time is set to be long enough for a wireless communication unit (105) to perform power measurements of the pilot signal. This reduces the likelihood of pilot signal interference in neighbouring cells. The access point (104) may also switch over to operating in a continuous pilot signal transmission mode in order to improve a handover or cell selection process. The access point (104) can also be arranged to transmit the mark:space ratio of the pilot signal for reception by a user equipment (105). This permits the user equipment (105) to modify its thresholds for RSCP and Ec/No calculations accordingly.

Description

NETWORK ELEMENTS, WIRELESS COMMUNICATION SYSTEM AND METHODS THEREFOR

Field of the invention

The field of this invention relates to network elements, a wireless communication system and methods therefor and particularly to methods for controlling pilot signal transmissions.

Background of the Invention

Wireless communication systems, such as Wireless Local Area Networks, (WLAN) and the 3rd Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTSTM), developed by the 3rd Generation Partnership Project (3GPPTM) (www.3gpp.org). The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Such macro cells utilise high power base stations (NodeBs in 3GPP parlance) to communicate with wireless communication units within a relatively large geographical coverage area.

Typically, wireless communication units, or User Equipment (UEs) as they are often referred to in 3G parlance, communicate with a Core Network (CN) of the 3G wireless communication system via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of radio network subsystems, each radio network subsystem comprising one or more cells to which UEs may attach, and thereby connect to the network. Each macro-cellular RNS further comprises a controller, in a form of a Radio Network Controller (RNC), operably coupled to the one or more Node Bs, via a so-called lub interface.

The second generation wireless communication system (2G), also known as GSM, is a well-established cellular, wireless communications technology whereby "base transceiver stations" (equivalent to the Node B's of the 3G system) and "mobile units" (user equipment) can transmit and receive voice and packet data. Several base transceiver stations are controlled by a Base Station Controller (BSC), equivalent to the RNC of 3G systems.

Communications systems and networks are developing towards a broadband and mobile system. The 3rd Generation Partnership Project has proposed a Long Term Evolution (LTE) solution, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), for a mobile access network, and a System Architecture Evolution (SAE) solution, namely, an Evolved Packet Core ( EPC), for a mobile core network. An evolved packet system (EPS) network provides only packet switching (PS) domain data access so a voice service is provided by a 2G or 3G Radio Access Network (RAN) and circuit switched (CS) domain network. User Equipment( UE) can access a CS domain core network through a 23/3GRAN such as the (Enhanced Data Rate for GSM Evolution, EDGE) Radio Access Network (Radio Access Network, GERAN) or a Universal Mobile Telecommunication System Terrestrial Radio Access Network (Universal Mobile Telecommunication System Terrestrial Radio Access Network, UTRAN), and access the EPC through the E-UTRAN.

Some user equipments have the capability to communicate with networks of differing radio access technologies. For example, a user equipment may be capable of operating within a UTRAN and within an E-UTRAN.

Lower power (and therefore smaller coverage area) cells are a recent development within the field of wireless cellular communication systems. Such small cells are effectively communication coverage areas supported by low power base stations. The terms "picocell" and "femtocell" are often used to mean a cell with a small coverage area, with the term femtocell being more commonly used with reference to residential small cells. Herein, the term" small cell" means any cell having a small coverage area and includes "picocells" and femtocells. The low power base stations which support small cells are referred to as Access points (AP's) with the term Home Node B (HNB's) or Evolved Node Node B (eHNB) identifying femtocell access points. Each small-cell has one Access point.

These small cells are intended to augment the wide area macro network and support communications to User Equipments in a restricted, for example, indoor environment. An additional benefit of small cells is that they can offload traffic from the macro network, thereby freeing up valuable macro network resources.

Typical applications for such Access Points include, by way of example, residential and commercial locations, communication hotspots', etc., whereby Access Points can be connected to a core network via, for example, the Internet using a broadband connection or the like. In this manner, small cells can be provided in a simple, scalable deployment in specific in-building locations where, for example, network congestion at the macro-cell level may be problematic.

An example of a typical AP for use within a 3GPP 3G system may comprise Node-B functionality and some aspects of Radio Network Controller (RNC) functionality as specified in 3GPP TS 25.467. An AP communicates with User Equipments (UE), via a wireless interface.

A HNB is an example of access point that provides a wireless interface for a user equipment connectivity. It provides a radio access network connectivity to a user equipment (UE) using the so- called luh interface to a network Access Controller, also known as a Home Node B Gateway (HNB-GW). One Access Controller (AC) can provide network connectivity of several HNB's to a core network.

Transmissions of reference pilot signals are frequently used in wireless communication systems. For example, in the cellular systems mentioned above, such as GSM or UMTS, the base stations transmit a reference or "pilot" signal that User Equipments may use to make power measurements. These measurements may be used to perform cell selection and relocation, as part of a "handover" operation, for example and in general provide an indication of a level of coverage provided by a particular cell. According to the UTRAN standard, such a pilot signal is known as a Common Pilot Indicator Channel (CPICH) and is a downlink channel, broadcast by an Access Point (or Node B or F-INB), usually at a constant power level amounting to between 5% and 15% of the total Access Point transmit power. A pilot channel transmitting at a constant power level can provide a fixed reference for a User Equipment and usually a number of additional common channels are also transmitted which are referenced to the pilot signal (with a fixed power offset, for example). A CPIOH comprises a known bit sequence. On receiving the OPICH, and extracting the primary scrambling code the User Equipment may then use the channel for RSCP (received signal code power) and Ec/No (signal chip power) measurements. The values of these power measurements, with respect to pre-configured thresholds, may be used by a User Equipment and/or core network elements in a handover operation. For example, if the Ec/No measurement from the cell currently serving a User equipment drops below a pre-configured value, and the Ec/No value of a neighbouring cell rises to a level above another pre-configured value, then a process may be put in place to handover the User Equipment from the serving cell to the neighbouring cell so that a communication between the User Equipment and the core network can be maintained.

However, a disadvantage of using pilot signals is that a relatively high level of interference is constantly generated by the pilot signals merely to support cell detection and selection. The generated interference is furthermore independent of the loading of the system and a substantial degree of interference is generated even by Access Points not currently serving any User Equipments. Although simply reducing the power of the CPICH would ameliorate the interference problem to some extent, this has the disadvantage of reducing the range at which a User equipment can detect a cell. There are two criteria for cell selection. RX Lev (i.e. the absolute power in dBm) and RX Qual (which is the interference measure). So if two Access Points transmit on the same frequency then the two CPICF-l's cause interference to each other. Furthermore, the measured RX Qual may not be sufficient to select the cell.

In the case of large numbers of small cells, each served by a low power Access Point which may support only very few User Equipments, for much of the time, such a small cell may be completely unloaded. Thus, the constant transmission of a CPICH signal imposes continuous interference on the surrounding cells' pilot signals which directly affects the quality of cell selection, reselection, handover or relocation. Furthermore, in small cell deployments, User Equipments are more likely to have smaller pathlosses to the small cells Access Point compared with a macrocell regardless of whether the User Equipment is allowed to access the small cell or not.

US2O1O/0022266 discloses methods for controlling pilot signal transmission power in one of several modes. In one mode, if no User Equipments are being supported, then the Access Point slowly varies the transmit power between two values. US2009/0280819 discloses a method for managing a pilot signal in accordance with a signal power profile. Known processes tend to be slow and therefore a User Equipment may not be able to detect an Access point for a relatively long period of time.

Thus, there exists a need for an improved method and apparatus for controlling pilot signal transmissions which mitigate, alleviate or eliminate one or more of the above mentioned disadvantages.

Summary of the invention

Aspects of the invention provide network elements, a cellular communication system and methods therefor as described in the appended claims.

According to a first aspect of the invention there is provided a method for controlling pilot signal transmissions in a cellular communications system, the method comprising, configuring an access point for transmission of a pilot signal for reception by a wireless communication unit, operating the access point to control a transmitted power of the pilot signal in a first mode of operation by switching the pilot signal periodically between a first transmission power level and a second transmission power level with a configurable mark: space ratio wherein the first transmission power level is maintained for a time period comparable with the time taken by the wireless communication unit to perform power measurements of the pilot signal.

In a preferred embodiment, the first mode of operation comprises switching the pilot signal between an "on" state and an "off" state with a configurable "on" time and a configurable "off" time, wherein the configurable "on" time is long enough for the wireless communication unit to perform power measurements of the pilot signal.

Hence, the power of the pilot signal may be periodically switched between a higher level and a lower level and the lower level may be zero.

In one example, the method may further comprise transmitting an indicator of the mark: space ratio (or the ratio of the configurable "on" time to the configurable "off' time) for reception by a wireless communication unit.

Optionally, the method may further comprise detecting if all wireless communication units that are authorised to access the access point are currently attached to said access point, and if so, adjusting the transmissions of the pilot signal so that said transmissions at the first transmission power level coincide with timeslots during which each of the wireless communication units is "listening" to the access point's broadcast channels.

The method may include operating the access point to switch from controlling the transmit power of the pilot signal in the first mode of operation to a second mode of operation in which the pilot signal is transmitted continuously. This second mode may be used when it is detected that a wireless communication unit requires access to the access point (eg. in a cell selection or handover process).

Switching to continuous transmission improves the selection or handover process. Detecting if a wireless communication unit requires access to the access point may comprise receiving an incoming call which requires the access point to send a paging message to the wireless communication unit. In another example, detecting if a wireless communication unit requires access to the access point may comprise receiving a random access message from the wireless communication unit.

The second mode may also be entered periodically for a pre-set period of time so that an unattached User Equipment has a greater chance of "seeing" the access point.

The invention is particularly useful in cases where the access point serves a small cell, eg. a femtocell. While continuity of a CPIOH transmission from a base station serving a macrocell is useful for allowing fast attachment to the core network, a compromise can be made between this continuity and the pilot signal "pollution" contribution of an access point (serving a small cell) on surrounding cells.

In known systems, the high and low levels of a varying pilot signal transmission power are maintained for a relatively long period of time. In contrast and advantageously, the present invention ensures that a pilot signal at a reasonable level is detectable all the time (from the point of view of a UE). In known systems, a UE in the vicinity of an Access Point (AP) will need to wait until the AP switches to the high pilot level in order to discover the AP, while with the present invention the UE will always see" the AP (with slightly lower power level, depending on the mark:space ratio) because of the comparatively fast switching between high and low levels (or the On and Off states).

According to a second aspect of the invention, there is provided an access point for supporting communication to and from a wireless communication unit in a cellular communication system wherein the access point is arranged to transmit a pilot signal for reception by the wireless communication unit and wherein the access point is further arranged to control the transmit power of the pilot signal in a first mode of operation in which the pilot signal is switched between a first transmission power level and a second transmission power level with a configurable mark: space ratio, wherein the first transmission power level is maintained for a time period comparable with the time taken by the wireless communication unit to perform power measurements of the pilot signal.

In a preferred embodiment, the access point is arranged to control a transmit power of the pilot signal in a first mode of operation by switching the pilot signal between an "on" state and an "off' state with a configurable "on" time, configurable "off' time, said configurable "on" time being long enough for the wireless communication unit to perform power measurements of the pilot signal.

Optionally, the access point may be further arranged to transmit an indicator of said mark:space ratio (or the ratio of the configurable "on" time to the configurable off' time) for reception by a wireless communication unit.

In a further embodiment, the access point may be arranged to determine if all wireless communication units that are authorised to access the access point are currently attached to it and if so, to adjust the transmissions of the pilot signal so that said transmissions at the first transmission power level coincide with operating timeslots of the wireless communication units.

The access point may be arranged to control the transmit power of the pilot signal in a second mode of operation in which the pilot signal is transmitted continuously. It may be arranged to do this when a request for access of a wireless communication unit (by way of a cell selection process or handover process, for example, is received.

According to a third aspect of the invention, there is provided a wireless communication unit arranged to receive a pilot signal from an access point in a wireless communication system and to receive an indicator of a mark:space ratio of said pilot signal, wherein the wireless communication unit includes a signal processor for adjusting measurement thresholds depending on said mark:space ratio. The signal processor may be incorporated in an integrated circuit.

According to a fourth aspect of the invention there is provided a wireless communication system arranged to support the method, access point and wireless communication unit of the above aspects According to a fifth aspect of the invention, there is provided a tangible computer program product having executable program code stored thereon for executing a process to perform a method for controlling pilot signal transmissions in accordance with the first aspect.

The tangible computer program product may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory These and other aspects, features and advantages of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter.

Brief Description of the Drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the fi9ures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

FIG. I illustrates a part of a cellular communication system operating in accordance with example embodiments; and FIG. 2 is a simplified flow chart of a method of operating an access point in a cellular communication system in accordance with an example embodiment.

Detailed Description

The inventive concept finds particular applicability in a cellular communication system that comprises a combination of small cells and macro cells. However, it will be appreciated by those skilled in the art that the invention is not limited to cellular mobile systems and can be equally applicable to other wireless systems, WLAN for example, which transmit a pilot signal.

Those skilled in the art will recognize and appreciate that the specifics of the specific examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings. For example, since the inventive concepts do not depend on any particular radio access technology (RAT), it is envisaged that the inventive concepts can be applied to 28 and LTE technologies or other RAT's or combinations thereof although 3G systems are shown in the embodiments. As such, other alternative implementations within cellular communication systems conforming to different standards are contemplated and are within the scope of the various teachings described.

Referring now to FIG. 1, an example of a 3G wireless communication system operating in accordance with some embodiments of the invention is illustrated and indicated generally at 100.

The system 100 comprises a small 3G cell A and a 3G macrocell B. Cell A may be a femtocell supporting a small residential or office location, for example. Cells A and B are neighbouring cells whose areas of coverage may overlap to some extent.

A core network of the wireless communication system of Fig. 1 includes a Gateway General Packet Radio System (GFRS) Support Node (GGSN) 101 and a Serving GPRS Support Node (SGSN) 102. The GGSN1O1 or SGSN 102 is responsible for interfacing the wireless communication system 100 with a packet data network, for example a Public Switched Data Network (PSDN), (such as the Internet) or a Public Switched Telephone Network (PSTN). The SSGN 102 performs a routing and tunnelling function for traffic to and from the cells A, B, while the GGSN 102 links with external packet networks. In an Evolved Packet Core, the equivalent node ito a GSGN is a Packet Gateway (P-GW).

The small cell A is linked to the SGSN by way of lu-PS and luh links via a 3G Home Node B Gateway (HNB-GW) 103. The small cell A is served by a network element in the form of an Access Point (AP)/I-lome Node B 104. As will be appreciated by the skilled artisan, an Access Point 104, may be a communication element that facilitates access to a communication network via a communication cell, such as a femto-cell. One application is that an AP may be purchased by a member of the public and installed in their home. The AP may then be connected to the HNB-GW 103 over the owner's broadband Internet connection. Although there are no standard criteria for the functional components of an AP, an example of a typical AP for use within a 3GPP 3G system may comprise Node-B functionality and some aspects of Radio Network Controller (RNC) functionality as specified in 3GPP TS 25.467. The AP 104 incorporates transmitting and receiving circuitry for enabling communication with User Equipments (UE's) such as UE 105 via a wireless interface.

The 3G macrocell B is served by a node B 106 which is controlled by a radio network controller (RNC) 107. The RNC 107 is linked to the SGSN 102 and to a mobile switching centre 108.

The MSC 108 is also linked to the HNB-GW 103.

The UE 105 is also capable of communicating wirelessly with the node B 107 of 3G macrocell B. the UE 105 is provided with a processing module 110 whose function will be explained below.

Initially, no UE's are attached to the small cell A and UE 105 is in a call supported by the macrocell B. The Access Point 104 is in a first mode of operation whereby its CPICH is transmitted at a configured transmission power for X transmission time intervals (where X is a positive integer number) that are sufficient for a typical UE to read and measure the CPICH after detecting and decoding the synchronisation channels for cell selection/reselection or measurement during a handover preparation process (from macrocell B to small cell A for example). For the remaining transmission time intervals the CPICH is not transmitted. The period of this switching process may be lOOms, for example. The "on time" may be SOms and the "off time" may be SOms in one example which results in a reduction in OPICH interference by half (3dB). In this first mode of operation, because the average CPICH power of the Access Point 104 is reduced then it is less likely to cause any " Pilot pollution" to any UE's that might be in an active call in the macrocell B. The ratio between transmission times in which OPICH is transmitted and those in which it is not (ie. a mark:space ratio) is set so that the resulting averaged RSCP and Ec/No measurements performed by a UE do not drop more than a certain level (in dBs for example) below the actual OPICH (ie. a Pmax value) when CPICH is actually being transmitted. In this first mode, of the ratio between active CPICH and non-active CPICH (mark:space ratio) can be transmitted by the Access Point 104 as part of a broadcast channel content so that UEs which go as far as reading such channel can modify their RSCP and Ec/No calculations accordingly.

The Access Point 104 may be configured to periodically switch out of the first mode and into a second mode of operation and then back into the first mode again after a pre-configured time period.

In the second mode, the CPICH is broadcast continuously. This allows for improved cell detection and measurement by the UE 105.

As an example, while still in the call in the macrocell B, UE 105 moves away from node B 106 and closer to the Access Point 104 such that it is able to detect the Access Point 104 during the time when the latter transitions into its second mode of operation. It may also get close enough to the Access point 104 to detect the CPICH transmission in the on/off, first mode of operation. The UE 105 also detects the broadcast mark:space ratio of the CPICH which the Access Point 104 is using in its first mode of operation. In response to the UE 105 receiving the broadcast mark;space ratio, the signal processor 110 in the UE 105 adjusts its RSCP and Ec/No thresholds so that it can assess whether or not the small cell A is a potential handover target. If the UE 105 did not make these adjustments, then when the Access Point 104 reverts to its first mode of operation, the UE 105 will be detecting a lower CPICH power than expected, so it would disregard the Access Point, (whereas, if the OPICH were being continuously transmitted, then the UE 105 would identify the cell A as a suitable handover target). After the UE 105 has made the adjustments and performed and reported the (conventional) measurements to the RNC 107 via the node B 106, the RNC 107 may decide that a handover from cell B to cell A should be made. In such a case, the Access Point 104 is notified and, in addition to the conventional procedures for a handover, it may re-enter its second mode of operation in order to improve the quality of the handover process. When handover is complete, the Access Point 104 may revert to the first mode of operation.

In another example of operation, the Access Point 104 is pre-configured with a "whitelist" of subscribers (ie. UE's that are authorised to use the particular Access Point 104 which supports the small cell A). It is also capable of detecting when all the UE's in the whitelist are attached to it. In this condition then, when all authorised UE's are attached, this means that no further UE's will be requesting attachment or handover. Therefore, there is no need for the Access Point 104 to enter the second mode of operation.Further, as is conventional, the Access Point 104 will be aware of the paging slots assigned to every attached UE. So while this condition persists, the Access Point 104 can adjust the CPICH on/off cycle so that the pilot signal is transmitted only when an attached UE is planned to come out of its DRX (discontinuous reception) mode to look for any Paging Indicator Channels that are being broadcast and to take measurements of its serving cell and neighbouring cells. UE's may make several measurements of the cell and average them. The mark:space ratio may be adjusted so that the "on" time of the CPICH transmission is set to be longer than this averaging period..

For (the whitelisted) UE's that are attached to the Access Point 104, the small cell A needs to look like a normal cell and so when Paging or Cell Broadcast messages are sent, then the Access Point 104 powers up the CPICH level to normal "ON" levels.

When non-attached UE's enter the vicinity of the Access Point 104 or pass through the coverage area of small cell A, then they are operating on an asynchronous timebase (compared with the Access Point 104) if they are attached to to the Macroell B and so will typically see the power level of the CPICH broadcast by the Access Point 104 at a reduced" level (while the Access Point is operating in the first mode) If such a UE should happen to make measurements when the Access Point is operating in its second mode (continuous transmission of the CPICH) then it is likely that the UE would cause a TReselection timer to run (typically 1-2 seconds) for which the UE must see the Access Point 104 cell better' than the macrocell B. In a case where this condition is satisfied, then the UE might try to select the Access Point 104 and perform a location update. If it did try to select the Access Point 104 but was not on the whitelist, then its request for selection would be rejected If an allowed UE (ie. one on the whitelist) is to be able to "see" the small cell A, then every two minutes or so and for a predetermined length of time, typically 30s in one example the Access Point will go to a "continuous ON" state (second mode of operation) to give UE's the best chance of detecting the CPICH. This means that allowed (whitelist) UEs will get an opportunity to "camp on" if they linger around the cell long enough. The result is that passer-by UE's will not see the cell as attractive, whereas slow moving, lingering UE's will.

Referring now to FIG. 2, there is illustrated a simplified flow chart 200 of an example of a method of operating an Access Point (AP) in a wireless communication system. The flow chart of FIG. 2 starts at 201 where the AP is pre-configured with pilot signal (CPICH) start-up values. These values include an "on" time and an "off" time of the pilot signal for the AP operating in a first mode. The ratio of these times is a mark:space ratio of the pilot signal. The start-up values also include a maximum power level for the pilot signal, a time ""t" for which the AP operates in the first mode before entering a second mode where the pilot signal is transmitted continuously, and a time T for which the AP remains in the second mode before reverting to the first mode.

At 202 the AP is activated and enters the first mode of operation where the pilot signal is switched between on and off states with the pre-set mark;space ratio. The AP also broadcasts the mark;space ratio. If, at 203, no UE's are detected as requiring access to the AP, then the AP continues in its first mode until time t has expired whereupon it enters the second mode of operation until time T has expired then reverts to the first mode.

If at 203 it is detected that a UE requires access to the AP (by receiving an incoming call requiring sending a paging message to the UE, or by receiving a random access message from the UE, for example) and that the UE is on the AP's whitelist, then the AP enters the second mode of operation where the pilot signal is transmitted continuously. Access to the AP may be required by UE selecting the AP for attachment or from a UE already attached to a neighbouring cell but requiring handover to the AP.

The AP continues to operate in the second mode until the attachment (or handover) process is completed: whereupon at 207, it reverts to the first mode. The cycle repeats from 203 onwards until the AP detects (at 208) that all whitelisted UE's are attached to it (by camping on the AP and executing a conventional location update procedure through the AP, for example). At this point in the process, the AP adjusts (209) the pilot signal transmissions based on the paging time slots of the attached UE's, ie. the AP adjusts the CPICH on/off cycle so that the pilot signal is transmitted only when a UE is planned to come out of its DRX (discontinuous reception) mode.

The signal processing functionality of the embodiments of the invention, particularly the access point 104 or the signal processor 110 in the UE 105, may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface, such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

In this document, the terms computer program product', computer-readable medium' and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally referred to as computer program code' (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at -12-least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices. Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term comprising' does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to a', an', first', second', etc. do not preclude a plurality.

Claims (18)

1. Claims 1. A method (200) for controlling pilot signal transmissions in a cellular communications system (100), the method comprising; configuring (201) an access point (104) for transmission of a pilot signal for reception by a wireless communication unit (105), operating the access point (104) to control a transmitted power of the pilot signal in a first mode of operation (202) by switching the pilot signal periodically between a first transmission power level and a second transmission power level with a configurable mark: space ratio wherein the first transmission power level is maintained for a time period comparable with the time taken by the wireless communication unit (105) to perform power measurements of the pilot signal.
2. 2. The method (200) of claim 1 wherein operating the access point (104) to control a transmit power of the pilot signal in a first mode of operation (202) comprises switching the pilot signal periodically between an "on" state and an "off' state with a configurable "on" time and a configurable "off" time, wherein the configurable "on" time is long enough for the wireless communication unit (105) to perform power measurements of the pilot signal.
3. 3. The method of claim 1 or claim 2 comprising transmitting (204) an indication of the mark: space ratio for reception by a wireless communication unit (105).
4. 4. The method of any preceding claim comprising; detecting (208) if all wireless communication units (105) that are authorised to access the access point (104) are currently attached to said access point (104), and if so, adjusting (209) the transmissions of the pilot signal so that said transmissions at the first transmission power level coincide with operating timeslots of the wireless communication units.
5. 5. The method of any preceding claim comprising; operating the access point (104) to switch from controlling the transmit power of the pilot signal in the first mode of operation to a second mode of operation (205) in which the pilot signal is transmitted continuously.
6. 6. The method of claim 5 comprising; detecting (203) if a wireless communication unit (105) requires access to the access point (104), and if so, operating the access point (104) to control a transmit power of the pilot signal in a second mode of operation (206) in which the pilot signal is transmitted continuously. -14-
7. 7. The method of claim 6 wherein detecting (203) if a wireless communication unit (105) requires access to the access point (104) comprises receiving an incoming call which requires the access point to send a paging message to the wireless communication unit (105).
8. 8. The method of claim 6 wherein detecting (203) if a wireless communication unit (105) requires access to the access point (104) comprises receiving a random access message from the wireless communication unit (105).
9. 9. An access point (104) for supporting communication to and from a wireless communication unit (105) in a cellular communication system (100) wherein the access point (104) is arranged to transmit a pilot signal for reception by the wireless communication unit (105) and wherein the access point (104) is further arranged to control a transmit power of the pilot signal in a first mode of operation in which the pilot signal is switched between a first transmission power level and a second transmission power level with a configurable mark: space ratio, wherein the first transmission power level is maintained for a time period comparable with the time taken by the wireless communication unit (105) to perform power measurements of the pilot signal.
10. 10. The access point (104) of claim 9 wherein the access point is arranged to control the transmit power of the pilot signal in a first mode of operation by switching the pilot signal between an "on" state and an "off" state with a configurable "on" time and configurable "off' time, said configurable "on" time being long enough for the wireless communication unit (105) to perform power measurements of the pilot signal.
11. 11. The access point (104) of either claim 9 or claim 10 and further arranged to transmit an indicator of the mark: space ratio for reception by a wireless communication unit (105).
12. 12. The access point (104) of any of claims 9 to 11 and further arranged to detect if all wireless communication units (105) that are authorised to access the access point (104) are currently attached to said access point (104), and if so, to adjust the transmissions of the pilot signal so that said transmissions at the first transmission power level coincide with operating timeslots of the wireless communication units (105).
13. 13. The access point (104) of any of claims 9 to 13 and further arranged to control the transmit power of the pilot signal in a second mode of operation in which the pilot signal is transmitted continuously.
14. 14. The access point (104) of claim 13 being further arranged to operate in said second mode of operation when a request for access to the access point (104) of a wireless communication unit is received by said access point (104).
15. 15. A wireless communication unit (105) arranged to receive a pilot signal from an access point (104) in a wireless communication system (100) and to receive an indicator of a mark:space ratio of said pilot signal, wherein the wireless communication unit (105) includes a signal processor (110) for adjusting measurement thresholds depending on said mark:space ratio.
16. 16. A wireless communication system (100) adapted to support any of the methods of claims 1 to 8 or the access point (104) of claims 9 to 14 or the wireless communication unit (105) of claim 15.
17. 17. A tangible computer program product (104) having executable program code stored thereon for executing a process to perform a method in accordance with any of claims Ito 8.
18. 18. The tangible computer program product of claim 17 wherein the tangible computer program product comprises at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.