GB2518621A

GB2518621A - Telecommunications system and method

Info

Publication number: GB2518621A
Application number: GB1317025.3A
Authority: GB
Inventors: Islam Essam-Hosny; Ahmed Hamdy-Ibrahim
Original assignee: Vodafone Egypt
Current assignee: Vodafone Egypt
Priority date: 2013-09-25
Filing date: 2013-09-25
Publication date: 2015-04-01
Also published as: WO2015044661A3; GB201317025D0; WO2015044661A2

Abstract

A method of operating a telecommunications repeater including a plurality of antenna modules, includes: receiving signals broadcast by a plurality of cells on their respective broadcast frequency channel, BCCH; and, performing parameter measurements on at least a portion of each of the received broadcast signals, in order to determine a cell from the plurality of cells to select. The method further includes selecting one of the antenna modules based upon results of the parameter measurements, and using only the selected antenna module for repeating incoming and/or outgoing signals from the repeater. Parameter measurements are process to determine a cell that provides the best signal coverage and the antenna module which provides the best received signals for the determined cell is selected. Parameter measurements on signals broadcast by the plurality of cells are performed at predetermined regular intervals based upon a determined rate of movement of a movable object. Parameter measurements performed on the received signals relate to the C2 parameter. Suitable for use in cruise boats where the signal quality from the outdoor environment is affected by interference, wherein prior art repeaters magnify the interference in the repeated signal.

Description

Telecommunications System and Method The present invention relates to a telecommunications repeater and a method of operating the same. More particularly the present invention relates to an add-on device for a telecommunications repeater, which is adapted to enhance the functionality of the repeater.

Background

Repeaters are currently used in conjunction with mobile telecommunications networks, in order to enhance coverage in areas where signal transmission is restricted, typically due to topographical obstacles including man-made obstructions such as buildings. In general, in areas where mobile terminals are unable to connect with a network base station, or only receive weak signals from the nearest base station, repeaters can are used to as an intermediary receiver/transmitter in order to amplify radio signals in the affected area.

Repeaters may be located anywhere where an amplified radio signal is required.

They may be wired or wireless, and located on or in static or moving objects. One particular application of such repeaters is in relation to ocean and river cruise boats.

Since cruise boats are mobile, the access to telecommunications base stations will be regularly changing and not always reliable. Cruise boats therefore often have one or more repeaters installed in order to enhance their passenger's telecommunications experience.

Repeaters operate by enhancing wireless coverage, particularly indoor coverage.

This serves to minimise the dropped calls users suffer when coverage would otherwise be poor. Also, the repeaters serve to enhance the voice quality of the call by improving the repeated power (i.e. C/I).

In a typical known configuration for amplifying radio signals indoors, a repeater is attached to a single Yaggi antenna, which is fixed in a given direction. The antenna therefore forwards all received signals from the given focal direction outdoors to the repeater, which magnifies and repeats them all indoors.

One problem with this solution is that where the signals from the outdoor environment are affected by interference, then that interference is also magnified in the repeated signal. This interference can badly affect voice/sound quality and can also cause calls to be dropped. This problem is exacerbated with cruise boat repeaters, as the normal losses which would apply to interfering signals from distant base stations do not occur (because of water guiding effect). As a result the interference level is relatively high for cruise boat repeaters in the vicinity of water, as compared to interference levels in other environments.

There is therefore a need to overcome or at least ameliorate one of the problems of the prior art. In particular, there is a need for a repeater that has improved functionality, particularly in regard to the quality of the repeated signals.

Summary of the Invention

According to one aspect the present invention provides the features as defined in the claims.

According to another aspect, the present invention provides a method of operating a telecommunications repeater including a plurality of antenna modules, the method including: receiving a plurality of signals broadcast by a plurality of cells on one or more particular frequencies, such that at the one or more particular frequencies the signals are transmitted at, or substantially at, maximum cell power; performing parameter measurements on at least a portion of each of the received signals, such that the parameter measurements are performed on signals representing each of the cells at, or substantially at, maximum cell power; selecting one of the antenna modules based upon results of the parameter measurements; using only the selected antenna module for repeating incoming and/or outgoing signals from the repeater.

Importantly it has been realised that the reason existing repeaters did not consistently provide a useful or even workable coverage, was that the outdoor antennas were collecting all detectable radio signals and repeating/amplifying all of those detected signals, regardless of the signals being of a good or bad quality. In other words, it has been realised that the repeaters were amplifying interference in addition to the signals, which was undesirable.

In this manner, the present invention addresses this problem as it enables the cell in the vicinity of the repeater that has the best signal strength to be selected. In this regard, it has advantageously been determined that performing measurements on each cell's broadcast channel provides the most accurate approach for cell selection, as this is the frequency or frequencies which most consistently transmit signals at a maximum cell power.

Once the cell with the best donor cell has been selected, correspondingly, the present invention enables lesser quality cells, which may cause call interference, to be rejected. Importantly the present invention utilises current (i.e. real time) measurements to make this determination and selection. This ensures that the cell selection is accurate and based upon the actual external conditions/environment.

This improves the reliability of the overall system, and is particularly important for repeaters located on movable vessels/vehicles.

This embodiment of the invention may be implemented using a micro-controller circuit with a number of selective antennas and RF switches. Where such a micro-controller is utilised, it is able to apply a selection algorithm in accordance with the invention in order to select the best donor cell. In this way cells that may affect the call negatively, such as by leading calls to be dropped or voice quality to deteriorate, are effectively rejected. This therefore enables interference on mobile terminals using the repeater to be suppressed or at least minimised, leading to a better operating environment for the handsets.

An addition advantage of this embodiment of the invention is that it enables data connections (e.g. EDGE) to be more stable.

In a still further aspect, the present invention provides a method of operating a telecommunications repeater located on a movable object, the method including: determining a current rate of movement of the moveable object; using the determined current rate of movement to determine a time interval at which to perform parameter measurements on received signals broadcast by a plurality of cells; and regularly performing parameter measurements on the received signals at the determined time interval.

Brief Description of the Drawings

Embodiments of the invention will now be described with reference to the Figures, in which: Figure 1 illustrates a schematic diagram of a repeater configuration according to an embodiment of the invention; Figure 2 illustrates a more detailed schematic diagram of a repeater configuration according to an embodiment of the invention; Figures 3A and 3B illustrate, respectively a graph of C/I on the BCCH carrier for a repeater according to the invention, and a corresponding graph for a prior art repeater; Figures 4A and 4B illustrate, respectively, a worst case of C/I for the repeater according to the invention and a corresponding graph for the prior art repeater; Figures 5A and 5B illustrate, respectively, a best case of C/I for the repeater according to the invention and a corresponding graph for the prior art repeater; Figures 6A and 6B illustrate, respectively, the Received Signal Level (RxLev) for the repeater according to the invention and a corresponding graph for the prior art repeater.

Detailed Description

A first embodiment of the invention will now be described with reference to Figure 1.

This Figure schematically illustrates a repeater associated with one or more repeating antennas and a plurality of receiving antennas. The receiving antennas are configured to pick up radio signals to be amplified by the repeater, and the repeating antennas are typically internal antennas (e.g. internal to a building or a moving vehicle/vessel) for transmitted the amplified signals. The receiving antennas are typically external to any vessel, vehicle or building to maximise their receiving capabilities.

Further, these receiving antennas are typically directional antennas, with each antenna covering a particular angular range. For example, if three antennas are used, each antenna could cover a portion of a 360 degree region (e.g. a 60 degree portion). It is to be appreciated that it is not essential that the antennas cover a 360 degree region, and that a smaller region could be covered (for example, for a cruise boat application, the receiving antennas could cover a region just focussing towards the shoreline). Similarly, it is also not essential that the angular range of each antenna is the same, or that the range of each antenna is non-overlapping.

In this embodiment of the invention, the inventive functionality is provided by an add-on to the repeater, which is provided between the main repeater circuitry and the one or more external receiving antennas.

Figure 2 provides a more detailed schematic illustration of the overall repeater according to this embodiment of the invention. The external receiving antennas of the repeater comprise first and second fixed sector antennas. It is to be appreciated that any number of these fixed sector antennas may be utilised, and that the present embodiment shows two for illustrative purposes only. Each of these antennas is configured to receive radio signals, convert these signals to an electrical signal which is output from the antenna. The output is split via a two-way splitter (or Tapper), with one split output being transmitted towards a microcontroller system and the other output towards a multiplexer, which acts as a switch to regulate which antenna output is provided to the repeater.

Now the signals received by the external antennas will be signals broadcast from base stations in the vicinity. The broadcast signals include a base station identifier and are broadcast on a particular frequency. The identifier/frequency combination for each base station is unique. Ideally all base station in a given area broadcast on the same frequency but this is not essential.

The signals received by the antennas are transmitted towards the microcontroller system via a radio module. Each radio module is responsible for measuring one or more parameters in relation to the signals received by its associated antenna.

Typically the radio modules will keep a running average of the received signal level.

In this embodiment of the invention, the measured parameter is preferably an indication of signal quality. The parameter Cl could be used, but ideally the measured parameter is C2.

In this regard Cl depends on: -received signal level (typically averaged); -the parameter rxLevAccessMin, which is broadcast on the Broadcast Control Channel (BCCH), and is related to the minimum signal that the operator wants the network to receive when being initially accessed by a mobile terminal.

-the parameter msTxPwrMaxCCH, which is also broadcast on the BCCH, and is the maximum power that a mobile terminal may use when initially accessing the network; and -the maximum power of the MS.

C2 is a GSM parameter typically utilised by mobile terminals in the idle state for assessing cell selection and reselection. It is advantageous as when applied in hierarchical cell structures, as it keeps fast moving terminals in an upper layer and slow moving MS in micro cells. C2 is essentially an improved version of Cl, and is defined as follows: C2 = Cl + Cell_Reselect_Offset (CR0) -Temp_Offset (TO) (1) (when T< PENALTY_TIME) = Cl + CR0 (dB) (otherwise) 02 defines the measured signal strength plus a hysteresis that decreases by time to smooth any sudden changes in radio conditions, and an offset that is typically predefined. It is assumed that a fast moving mobile terminal passes through the micro cell before PENALTY_TIME is reached. This efficiently prevents unnecessary location updates and thus saves network signalling capacity.

As indicated previously, C2 is a parameter typically utilised for cell reselection by idle mobile terminals. This parameter has been chosen as the most preferable parameter to measure when selecting a suitable base station for the repeater to utilise, as it has been advantageously determined that the conditions an idle mode terminal would experience are a better indication of actual network conditions, as compared to comparable measurements that would be made in regard to a terminal in active mode.

In this regard, using 02 the radio modules take measurements and read the broadcasted messages sent by each cell on its broadcast frequency channel (BCCH) which are transmitted at the maximum cell power (or at substantially maximum cell power). These conditions are preferable over the dedicated/active mode conditions, as in dedicated mode, mobile terminals measure more than one frequency (i.e. more than just the broadcast frequency) and these other frequencies are controlled by a power control function. When measuring signal quality, it is not ideal that the power control function is operational since it makes dynamic changes to the signal level, resulting in a less accurate indication of actual coverage level.

Further, making use of just one frequency (e.g. the BCCH frequency) is advantageous, because frequencies transmitters generally combine cell frequencies.

This combining does not accurately reflect signal strengths from individual frequencies (i.e. a combining loss). The BCCH frequency, however is not combined with the other frequencies and accordingly does not suffer from the same problem.

This would again mean that measuring more than one frequency, as per the active mode approach, would result in a less accurate indication of actual coverage.

Accordingly, it has been advantageously determined that measuring signal quality using the signal parameter 02 provides a more consistent and comparable benchmark for signal quality.

It is to be appreciated that absolute signal strength could be used but it is less preferable as it is unstable, even for repeaters located on static objects. For instance, if absolute signal strength was utilised as the measured parameter to decide which antenna would be the serving one, for cells that are located on borders of location areas (i.e. where there are competing cells), the instability of the absolute signal strength parameter used by the repeater would force every mobile using the repeater to make several unneeded location area updates, resulting in too much signalling traffic and also potentially registration failures by the terminals, resulting in unreachable users. The 02 parameter is more preferable as it addresses this instability issue.

Returning to Figure 2, these parameter measurements are then fed to the microcontroller system. The measurements may be fed automatically, or alternatively, they may be transmitted upon the radio modules receiving a command/request from the microcontroller.

The microcontroller is configured to compare the parameter measurements in respect of each of the antennas. By comparing the measurements, the microcontroller will be able to determine the cell that is providing the best signal level and the antenna that receives the best signals from this cell. The microcontroller will then select this determined antenna.

Based upon this selection, the microcontroller system will then send a signal to the multiplexer in order to activate it so that it in turn chooses the selected antenna. In this way, the repeater effectively selects the best antenna, which receives the best signal quality from a cell to serve the repeater. Therefore, only signals from the selected antenna are sent to the repeating antennas for amplification. In this way, not only is the cell with the best signal quality (according to C2) chosen as the cell to be amplified and used for incoming and outgoing communications by users of the repeater, but the particular receiving antenna which corresponds to the best signals from that cell is chosen from the plurality of other receiving antennas.

In other words, this embodiment of the invention enables a single cell to be selected as a serving cell, with the least interference from surrounding cells, using signal quality measurements taken in real-time. By doing so, one antenna is also chosen, so that signals from only one direction/region are receivable by the repeater, effectively rejecting signals from the other directions/regions.

This embodiment of the invention will operate best with a large number of antennas, as increasing the number of antennas will typically raise the accuracy of the selection. However, a large number of antennas of course has greater complexity and cost, so the ideal number of antennas is a balance between the two considerations.

To illustrate the effectiveness of this embodiment of the invention, the repeater configuration was tested alongside a standard repeater (i.e. the prior art repeater is one which is connected directly to an Omni antenna which amplifies signals from all directions and from all cells). In this regard, Figure 3A illustrates a graph of C/I on the BCCH carrier for the repeater according to the invention and Figure 3B illustrates a corresponding graph for a repeater of the prior art. This illustrates that, we have been able to gain an enhancement of around 52% in the C/I ratio on the BCCH carrier, with around an 11% enhancement in the standard deviation.

Figures 4A and 4B illustrate the worst case of C/I for the repeater according to the invention and the standard repeater respectively. From these Figures it can be seen that even in the worst case scenario, the repeater of the present invention provided an improvement over the prior art repeater. The improvement was about a 6% improvement.

Figures 5A and 5B illustrate the best case of C/I for the repeater according to the invention and the standard repeater respectively. From these Figures it can be seen that in the best case scenario, although the best C/I did not change on average, the standard deviation was less for the repeater of the present invention, which means that it resulted in more samples with high C/I.

Figures 6A and 6B compare the Received Signal Level (RxLev) for the repeater according to the invention and the standard repeater respectively. Although we have achieved all the enhancements noted above, there was no significant change in the average received signal strength. Accordingly there is still a margin to enhance the coverage around 2.5dB by replacing the 2-way splitter with a 2-way tapper. This is because, the splitter used in the field test takes half of the received power from the antenna just to measure it (i.e. but not to serve). As a result the input of the repeater only receives half of the actual received signal power. This can be improved upon by using a splitter that splits the received power into two unequal parts, so that a smaller fraction is used for measurement purposes. For example, bu just taking a fifth of the received power for measurements four fifths of the received power will remain for use by the repeater.

Preferably the microcontroller system continues to repeatedly/periodically compare measurements from the different antennas in order to ensure that the users of the antenna are receiving the best signal quality available. Where the repeater is located on a moving vessel/vehicle, the frequency of the updates (or duration between updates) is ideally dependent upon the speed of the vessel.

A further aspect of the invention addresses this issue in relation to update regularity for cell reselection. This is because speeding the process up a lot or delaying the frequency unduly may cause problems. For instance, if the reselection update frequency is high, this would result in an increased signalling load on the base station (BSC) and the base station site which may impact the service. On the other hand, if the frequency is low, less reselection updates would occur which may cause a delay in the best cell selection and hence poor voice quality may occur until the next update.

It has been advantageously determined that the frequency of reselection updates should be chosen relative to the average speed of the vessel/vehicle and also the network site to site distance. Where carefully chosen in this manner, the number of unneeded handovers can be minimised, as well as the probability of a dropped call.

In other words, by managing the relationship between these parameters, the quality of calls can be enhanced. In one aspect, a reselection period of 3 seconds has been found to be optimal for cruise boats, based on an optimal distance resolution of updates of lOm and the average speed oficruise boats being 10-12km/h.

The embodiments of the invention have principally been described in relation to their use on cruise boats, however this is for illustrative purposes only. The embodiments of the invention may equally be applied to repeaters of other implementations, such as static repeaters in restaurants or gyms or repeaters implemented on other vehicles capable of motion, such as trains, aircraft, cars and buses.

The embodiments of the invention have particular relevance to static or slow moving vessels and vehicles. Where the vessels/vehicles are fast moving, some modifications could be made, such as speeding up the frequency of the reselection update cycle to cope with the faster speed of the vehicle, and adding more donor antennas on the vessel (based on the vessel moving) in order to enable a faster response to changes.

Still further, the embodiments of the invention have described separate radio modules and programmed microcontrollers for performing functionality important to the inventive concept. It is not however essential that these components be separate, and they may alternatively be pad of a unitary processing system.

Additionally, the embodiments of the invention have been described in relation to a 2G network and network components. Whilst this is a preferred implementation, the invention could also be adapted so as to be utilised in relation to other network configurations, particularly 3G networks.

Claims

CLAIMS: 1. A method of operating a telecommunications repeater including a plurality of antenna modules, the method including: receiving signals broadcast by a plurality of cells on their respective broadcast frequency channel, BCCH; performing parameter measurements on at least a portion of each of the received broadcast signals, in order to determine a cell from the plurality of cells to select.
2. The method of claim 1 further including: selecting one of the antenna modules based upon results of the parameter measurements; using only the selected antenna module for repeating incoming and/or outgoing signals from the repeater.
3. The method of any one preceding claim further including: determining the cell from the plurality of cells to select by processing the parameter measurements to determine a cell that provides the best signal coverage; and selecting one of the antenna modules based upon a determination as to which of the plurality of antenna modules provides the best received signals for that determined cell.
4. The method of any one preceding claim wherein the parameter measurements are performed on signals broadcast on the respective broadcast frequency channels, where these signals representing each of the cells operating at, or substantially at, maximum cell power.
5. The method of any one preceding claim wherein the parameter measurements performed on the received signals relate to the C2 parameter.
6. The method of any one preceding claim further including: subsequently performing further parameter measurements on signals broadcast by the plurality of cells at a predetermined regular interval; and determining whether to reselect an alternative antenna module based upon results of the further parameter measurements.
7. The method of claim 6, further including: determining a rate of movement of the movable object; and determining a time period for the regular interval based upon the determined rate of movement.
8. A telecommunications signal repeater including: a plurality of antennas, configured to receive signals broadcast by a plurality of cells on their respective broadcast frequency channel, BCCH; a processing system configured to: receive at least a portion of the received broadcast signals from the plurality of antennas; and perform parameter measurements on at least a portion of each of the received broadcast signals, which are usable in order to determine a cell from the plurality of cells to select.
9. The signal repeater of claim 8 wherein the processing system is further configured to: compare the parameter measurements relating to each of the antenna modules; and select one of the antenna modules, based upon the comparison so that only signals sent or received by the selected antenna module are handled by the repeater.
10. The signal repeater of claim 8 or 9 wherein the processing system is configured to perform parameter measurements relating to the C2 parameter on the received signals.
11. The signal repeater of claim 8, 9, or 10 wherein the processing system is further configured to: subsequently performing further parameter measurements on signals broadcast by the plurality of cells at a predetermined regular interval; and determining whether to reselect an alternative antenna module based upon results of the further parameter measurements.
12. The signal repeater of claim 11, wherein the telecommunications repeater is located on a movable object, and the processing system is further configured to: determine a rate of movement of the movable object; and determine a time period for the regular interval based upon the determined rate of movement.
13. A controller configured for use with a telecommunications signal repeater including a plurality of antennas configured to receive signals broadcast by a plurality of cells on their respective broadcast frequency channel, BCCH, the controller including: an input means configured to receive at least a portion of the received broadcast signals from the plurality of antennas; a processing means configured to: perform parameter measurements on the received broadcast signals; and select one of the antennas based upon results of the parameter measurements.
14. The controller of claim 13 wherein the processing means is further configured to subsequently performing further parameter measurements on signals broadcast by the plurality of cells at a predetermined regular interval; and determining whether to reselect an alternative antenna module based upon results of the further parameter measurements.
15. The controller of claim 14, wherein the telecommunications repeater is located on a movable object, and the processing system is further configured to: determine a rate of movement of the movable object; and determine a time period for the regular interval based upon the determined rate of movement.Amendments to the claims have been made as follows CLAIMS: 1 A method of operating a telecommunications repeater including a plurality of antenna modules, the method including: receiving signals broadcast by a plurality of cells on their respective broadcast frequency channel, BCCH; performing C2 parameter measurements on at least a portion of each of the received broadcast signals; and determining a cell from the plurality of cells to select, such that, based upon the C2 parameter measurements, the selected cell provides the best signal coverage; and selecting one of the antenna modules to utilise based upon results of the C2 parameter measurements.2. The method of claim 1 further including using only the selected antenna module for repeating incoming and/or outgoing signals from the repeater.3. The method of any one preceding claim further including determining the cell from the plurality of cells to select by processing the if)° parameter measurements to determine a cell that provides the best signal coverage; C'sJ and selecting one of the antenna modules based upon a determination as to which of the plurality of antenna modules provides the best received signals for that determined cell.4. The method of any one preceding claim wherein the parameter measurements are performed on signals broadcast on the respective broadcast frequency channels, where these signals representing each of the cells operating at, or substantially at, maximum cell power.5. The method of any one preceding claim further including: subsequently perhxming further parameter measurements on signals broadcast by the plurality of cells at a predetermined regular interval; and determining whether to reselect an alternative antenna module based upon results of the further parameter measurements.6. The method of claim 5, further including: determining a rate of movement of the movable object; and determining a time period for the regular interval based upon the determined s rate of movement.7. A telecommunications signal repeater including: a plurality of antennas, configured to receive signals broadcast by a plurality of cells on their respective broadcast frequency channel, BCCH; a processing system configured to: receive at least a portion of the received broadcast signals from the plurality of antennas; perform C2 parameter measurements on at least a portion of each of the received broadcast signals; is determining a cell from the plurality of cells to select, such that, based ct upon the C2 parameter measurements, the selected cell provides the best signal coverage; and selecting one of the antennas to utilise based upon results of the C2 parameter measurements LI° (\J 8. The signal repeater of claim 7 wherein the processing system is further configured to: compare the parameter measurements relating to each of the antenna modules; and select one of the antenna modules, based upon the comparison so that only signals sent or received by the selected antenna module are handled by the repeater.9. The signal repeater of claim 7 or S wherein the processing system is further configured to: subsequently performing further parameter measurements on signals broadcast by the plurality of cells at a predetermined regular interval; and determining whether to reselect an alternative antenna module based upon results of the further parameter measurements.10. The signal repeater of claim 9, wherein the telecommunications repeater is located on a movable object, and the processing system is further configured to: determine a rate of movement of the movable object; and determine a time period for the regular interval based upon the determined rate of movement.11. A controller configured for use with a telecommunications signal repeater including a plurality of antennas configured to receive signals broadcast by a plurality of cells on their respective broadcast frequency channel, BCCH, the controller including: an input means configured to receive at least a portion of the received broadcast signals from the plurality of antennas; a processing means configured to: perform C2 parameter measurements on the received broadcast signals; determine a cell from the plurality of cells to select, such that, based upon the C2 parameter measurements, the selected cell provides the best signal coverage; and select one of the antennas based upon results of the C2 parameter 1)20 measurements. (412. The controller of claim 11 wherein the processing means is further configured to subsequently performing further parameter measurements on signals broadcast by the plurality of cells at a predetermined regular interval; and determining whether to reselect an alternative antenna module based upon results of the further parameter measurements.13. The controller of claim 12, wherein the telecommunications repeater is located on a movable object, and the processing system is further configured to: determine a rate of movement of the movable object; and determine a time period for the regular interval based upon the determined rate of movement.