OVERLAY OF BEARERS IN A RADIO COMMUNICATION SYSTEM
A radio system having multiple bearers overlays a relatively narrowband bearer such as P25 on a relatively wideband bearer such as LTE, for transmission of both uplink and downlink signals. The wideband bearer uses a spectrum of subcarriers which form a set of radio frequency blocks. One or more blocks or other related parts of the spectrum may be allocated to the narrowband bearer. In some cases the narrowband bearer may push through the wideband allocation using a relatively high power to dominate signals transmitted by the wideband bearer. Voice calls such as emergency calls using the narrowband bearer may be prioritised.
This application is a divisional of U.S. patent application Ser. No. 13/542,147 filed 5 Jul. 2012, which claims priority to U.S. Provisional Patent Application Ser. No. 61/504,671 entitled “Overlay of Bearers in a Radio Communication System,” filed 5 Jul. 2011, the disclosures of which are incorporated herein by reference in their entireties.
FIELD OF THE INVENTIONThis invention relates to multi-bearer radio systems, such as systems which combine wideband and narrowband bearers. More particularly the invention relates to overlay techniques involving a relatively wideband bearer such as LTE (3GPP Long Term Evolution) and one or more relatively narrowband bearers such as P25 (APCO 25), Tetra, DMR (Digital Mobile Radio), or analogue LMR (Land Mobile Radio).
BACKGROUND INFORMATIONPublic safety agencies around the world are considering the deployment of broadband bearers such as LTE for improving data connectivity in their radio systems. Utility industries such as electricity distribution are also looking to exploit similar technology. The expectation is to deploy this relatively wideband technology to operate in parallel with existing narrow band systems such as P25. In the United States, the FCC has made specific frequency allocations supporting this model of deployment.
The LTE standard is based on OFDM (Orthogonal Frequency Division Multiplexing) of subcarriers and can be deployed in a number of channel bandwidths. A typical LTE FDD (Frequency Division Duplex) mode has uplink/downlink pairs including bandwidths of 20 MHz, 15 MHz, 10 MHz, 5 MHz, 3 MHz and 1.4 MHz. In the United States allocations of spectrum have been made representing 10+10 MHz in 3GPP band 14 for broadband operation. Specifically, the US has allocated frequencies 758 MHz to 768 MHz paired with 788 MHz to 798 MHz for broadband operation using LTE for Public Safety use. In addition, an allocation has been made for Public Safety for narrow band operation from 769 MHz to 775 MHz paired with 799 to 805 MHz. In other parts of the world private broadband allocations are being considered for use by public safety and critical infrastructure.
LTE coverage is made up of a number of frequency blocks, also referred to as resource blocks. An FDD 5 MHz channel has a set 25 resource blocks where each block is 180 kHz. Collectively the set of 25 blocks produces a bandwidth of 4.5 MHz within the 5 MHz channel with the 0.5 MHz remainder being used to contain the spectral skirts that operate within regulated emission masks. The channel is further divided into timeslots each of 0.5 ms, where a collection of 20 slots defines a frame. A resource block is therefore a block extending over a period which may include many timeslots. A set of frequency blocks contains many frames.
Each bearer in a wireless communication system requires a network of base stations to provide the channels over which users can communicate. The base stations are geographically located to provide coverage over a wide area within which the users are expected to move and require voice or data services. The users typically employ hand held or vehicle mounted terminals to communicate with the base stations. Each network generally includes a scheduler or controller which determines the timing and pathway of calls through the network. Bearer networks send control messages which are interpreted by the user terminals, in addition to voice and data messages which are sent between the users. In a trunked radio system a relatively large number of users share a relatively small number of frequencies, without being assigned to a fixed frequency for the duration of each call.
SUMMARY OF THE INVENTIONIt is an object of the invention to provide for improved use of available frequency spectrum in a multi-bearer radio system involving LTE and P25.
In one aspect the invention resides in a method of transmitting multiple radio bearer signals, including: providing a set of radio frequency blocks, allocating one or more frequency blocks for transmission of one or more signals using a first bearer, allocating one or more frequency blocks for transmission of one or more signals using a second bearer, and transmitting the signals using their allocated frequency blocks.
Preferably the first bearer provides a relatively wideband service for which multiple frequency blocks are allocated, while the second bearer provides a relatively narrowband service for which a single frequency block is allocated. The frequency blocks allocated to the first bearer are generally grouped together, but may be separated by one or more blocks allocated to the second bearer. Frequency blocks allocated to the second bearer may lie at one end of the set of blocks. When either bearer ceases transmission in some or all of an allocated portion of spectrum then the allocation available to the other bearer is generally increased. The signals transmitted using either bearer generally include both uplink signals transmitted by user terminals and downlink signals transmitted by base stations.
In another aspect the invention resides in a method of providing radio services using multiple bearer signals, including: providing a set of radio frequency blocks, allocating the frequency blocks for services using a first bearer, receiving a request for services using a second bearer, and re-allocating one or more of the frequency blocks for services using the second bearer. Signals such as voice calls and particularly emergency calls may therefore be prioritised.
In a further aspect the invention resides in a controller for a radio network, having a processor and memory, the memory containing instructions which cause the controller to carry out a method as outlined above.
In a further aspect the invention resides in a controller for terminal unit for a radio network, having a processor and memory, the memory containing instructions which cause the controller to select a bearer from multiple available bearers for transmission and reception of signals as outline above.
Preferred embodiments of the invention will be described with respect to the accompanying drawings, of which:
Referring to the drawings it will be appreciated the invention may be performed in a variety of ways using LTE and P25, and possibly a range of other communication bearers such as the DMR or LMR. Conventional details of these bearer systems need not be given in detail for a skilled reader. It will also be appreciated that the embodiments described here, using FDD 5 MHz and 10 MHz, are given by way of example only.
1A. P25 operating in a space created through reducing the bandwidth occupancy of LTE.
1B. P25 operating in a push through mode using a transmission power which is higher than relatively low powered LTE transmissions.
1C. P25 operating in the skirts of LTE transmissions.
1D. P25 operating within a disabled resource block of LTE.
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A P25 trunked controller may have a channel list with channels which are either standard P25 channels or overlay channels which exist somewhere in an LTE bandwidth allocation. A request for a channel may be received on a trunked control channel. If standard P25 channels are available, such as those available within the US narrowband allocation of 769 to 775 paired with 799 to 805 MHz, then the request may be assigned to a standard P25 channel. If no standard P25 channels are available or operating according to the local system policy then an alternative is to allocate P25 channels which spectrally exist within the LTE spectrum allocation, such as portions of available spectrum within the US broadband band allocation of 758 to 768 paired with 788 to 798 MHz. This assignment of frequency location can be made through interrogating a database of either instantaneous or preconfigured system usage.
The policy described so far involves assigning P25 channels to frequency locations in which minimal interference is created. An alternative policy may allow the P25 channel to be assigned either within the guard band of an active LTE transmission or within a currently unused resource block. If block 14 in
A policy of allocation within unused LTE spectrum is preferable as it creates minimal interference issues. Operating in the skirts of the LTE transmission is the next most favourable approach and it is estimated that around 300 to 400 kHz beyond the outer resource block enables operation with minimal interference between bearers. If neither standard P25 channel nor vacant LTE spectrum nor guard band are available then allocation may take place on an active LTE resource block but where this resource block is not carrying any user data. Generally, within an LTE resource block which is unused, the reference signals and control information within the frame should be turned off to minimise interference to the P25 receiver. The use of this resource block should then become restricted for the length of the P25 call. Because P25 channels are 12.5 kHz wide, multiple channels could fit within the 180 kHz bandwidth of an unused LTE resource block. Alternatively, a set of resource blocks may be unused and therefore P25 channels could be established in more than one position.
If no resource blocks are available within a reasonable time then a second assessment is made. If the option of P25 push through is enabled the P25 transmission may take place anyway over the top of the LTE transmission. This option may be enabled in the case of an emergency connection where connectivity via P25 overrides the importance of any data that may be on the current resource block. These modes can be applied for both downlink and uplink. If neither a resource block nor the option of transmitting in the skirts and the push through configuration is disabled then P25 access is denied.
The use of multiple possible P25 channels can be enabled through “scanning” which is a conventional technique. A P25 radio can either be tuned to a fixed frequency or can be configured to scan/vote to periodically look for activity across a range of frequencies. If relevant activity is detected the radio locks onto the particular channel reception.
Because P25 channels are 12.5 kHz wide, multiple channels can fit within the 180 kHz bandwidth of an unused LTE resource block. Alternatively, a set of resource blocks may be unused and therefore P25 channels could be established in more than one position. When resource blocks at one edge LTE transmission are shut down this is the equivalent to changing LTE operating between standard operating bandwidths, such as from 10 MHz to 5 MHz.
This represents an approach of dynamically expanding the mission critical P25 operation or the broadband operations according to which mode is required at the time. In this example we assume all standard P25 channels are busy and the only channel available is the overlay channel which is established through interrogating a commonly accessible database. The resource block available is one nominally assigned for LTE use but which is currently inactive due to the LTE bandwidth in that area being 5 MHz instead of 10 MHz at that time. Hence a P25 channel is assigned to the overlay position for the duration of the call. The database is also updated so that the broadband scheduler is informed to block access or reduce its bandwidth operation on this portion of the resource and the trunking controller is informed of success. It then sends the user to that channel.
Upon receiving a data connection request the scheduler may choose to allocate a user to a standard broadband position, such as portions of available spectrum within the US assigned broadband band allocation of 758 to 768 paired with 788 to 798 MHz. If however the P25 allocations in that area are not being used, as established through interrogating a database of usage, then the broadband system may expand its bandwidth of operation to extend across parts of the nominal narrow band allocation, for example 769 to 775 MHz paired with 799 to 805 MHz.
An equivalent process exists on the uplink where a multi-bearer device is in use. A controller is illustrated as the terminal end in
An analysis of the interference effects between P25 and LTE for sample overlay configurations of P25 and LTE can be provided. The analysis focuses upon the downlink. Generally there are three key forms of interference, co-channel (on channel), adjacent channel interference and wideband noise.
Considering an uplink case, given the US allocations and the standard P25 specifications, then on the uplink a P25 terminal could cause an interference problem over the adjacent LTE uplink (just 1 MHz away) if the P25 terminal was close to the LTE uplink antenna and the LTE terminal were far away. The LTE terminal will be operating power control anyway and its modulation and coding rate changes according to the observed interference level.
Referring to
We simply use one of the 3GPP base station masks as an example. This mask is applied to the scenario with an antenna gain of 14 dB and shown in blue. The specification assumes a 100 kHz b/w. The energy arriving in a 8.1 kHz bandwidth must be corrected. Assuming the path loss of over the P25 channel and the LTE channel are the same and the terminal is not so far away as to be below the P25 sensitivity limit then the C/I seen at the P25 receiver will be 61 dB. The C/I required for >=2% BER is typically 16 dB hence LTE will not significantly affect the performance of a P25 receiver.
In this case we have chosen a nominal value of 1% which typically represents a very good voice signal. Now we consider the effect of an LTE transmission occurring over 4.5 MHz in a channel allocation of 5 MHz. Also assume the transmission is fully occupied with data (worst possible case). LTE is now an interferer over P25.
The energy from an LTE transmission spilling into the narrow band of a typical P25 receiver would be approximately 27.4 dB (10*log10(8100/45e5) down compared to the total power of an LTE transmission. Given this and working with a co-channel requirement of 9 dB, we can estimate that an LTE transmission occurring over a P25 transmission could be 18.4 dB more powerful than P25 before causing a co-channel problem larger than P25. This means that for a co-located P25 and LTE site, as long as the P25 source is always more than 18.4 dB more powerful that LTE within the P25 bandwidth then P25 shall not observe a BER worse than 1% due to LTE interference.
Practically one would want a larger protection margin.
Consider the case of a P25 transmission at 47 dBm and an LTE transmission at 40 dBm. In this case the C/I seen at the P25 terminal up to 2 MHz offset from the LTE centre frequency would be approximate 47−12.6−14=20.4 dB which is close to the observed co-channel performance shown in
An individual LTE user can be allocated transmission resources within one or more resource blocks, time slotted within each resource block. Through disabling one or more RB within the LTE transmission allows the possibility of deploying P25 in this unused space. Measurements of a sample LTE system on the downlink in which one LTE resource block is no allocated to a user suggests that an unused resource block may be 10 dB down in is power compared to an fully used resource block. One might expect the power drop to be more substantial but it is important to remember that even in unused resource blocks, signalling and reference signals can still be present. The reference signals and control signals ideally need to be shut down to provide best performance on the P25 downlink. This means that P25 operating in an unused resource block would observe approximately a 30.4 dB C/I which is a good performance figure.
Claims
1. A method of managing resources in a multi bearer wireless communication system having a trunked radio system and a broadband data system, including:
- receiving a call request from a mobile terminal in the multi bearer communications system,
- determining that no trunked radio channels are currently available in the trunked radio system,
- determining that one or more frequency blocks are currently available in the broadband data system, and
- assigning a trunked radio channel in one of the available broadband frequency blocks for use in the call.
2. A method according to claim 1 further including:
- assigning the trunked radio channel in the available broadband frequency block in accordance with a policy which reduces interference with other broadband frequency blocks.
3. A method according to claim 2 wherein the policy provides a guard band between the trunked radio channel and active broadband frequency blocks.
4. A method according to claim 1 further including:
- assigning active broadband frequency blocks in accordance with a policy which reduces interference with the call in the trunked radio channel.
5. A method according to claim 1 wherein the mobile terminal combines trunked radio capability and broadband data capability.
6. A method according to claim 5 wherein the call request is made by the mobile terminal through the trunked radio system or through the broadband data system.
7. A method according to claim 1 further including:
- updating a database containing trunked radio channel information and broadband frequency block information with the assignment of the trunked radio channel.
8. A trunked controller for managing resources in a multi bearer wireless communication system having a trunked radio system and a broadband data system,
- the controller having a processor and memory, the memory containing software instructions for carrying out steps including:
- receiving a call request from a mobile terminal in the multi bearer communications system,
- determining that no trunked radio channels are currently available in the trunked radio system,
- determining that one or more frequency blocks are currently available in the broadband data system, and
- assigning a trunked radio channel in one of the available broadband frequency blocks for use in the call.
9. A trunked controller according to claim 8 wherein the memory contains software instructions for the steps of:
- reviewing policies relating to allocation of trunked radio channels and broadband frequency blocks, and
- assigning the trunked radio channel in the available broadband frequency block in accordance with a policy which reduces interference with other broadband frequency blocks.
10. A controller according to claim 9 wherein the policy provides a guard band between the trunked radio channel and active broadband frequency blocks.
11. A method of managing resources in a multi bearer wireless communication system having a trunked radio system and a broadband data system, including:
- receiving a broadband connection request from a user in the multi bearer communications system,
- determining that no frequency blocks are currently available in the broadband data system,
- determining that a number of adjacent trunked radio channels are currently available in the trunked radio system, and
- assigning a broadband frequency block over the available trunked radio channels for use in the connection request.
12. A method according to claim 11 further including:
- assigning the broadband frequency block over the available trunked radio channels in accordance with a policy which reduces interference from or with active trunked radio channels.
13. A method according to claim 12 wherein the policy provides a guard band between the broadband frequency block and the active trunked radio channels.
14. A method according to claim 11 further including:
- assigning active trunked radio channels in accordance with a policy which reduces interference with the broadband connection in the active broadband frequency block.
15. A method according to claim 11 wherein the connection request is sent from a mobile terminal having broadband data capability and trunked radio capability.
16. A broadband scheduler for managing resources in a multi bearer wireless communication system having a trunked radio system and a broadband data system,
- the scheduler having a processor and memory, the memory containing software instructions for carrying out steps including:
- receiving a broadband connection request from a user in the multi bearer communications system,
- determining that no frequency blocks are currently available in the broadband data system,
- determining that a number of adjacent trunked radio channels are currently available in the trunked radio system, and
- assigning a broadband frequency block over the available trunked radio channels for use in the connection request.
17. A scheduler according to claim 16 wherein the memory contains software instructions for the steps of:
- reviewing policies relating to allocation of broadband frequency blocks and trunked radio channels, and
- assigning the broadband frequency block in accordance with a policy which reduces interference with active trunked radio channels.
18. A scheduler according to claim 17 wherein the policy provides a guard band between the broadband frequency block and trunked radio channels.
19. A scheduler according to claim 16 wherein the memory contains software instructions for the step of:
- updating a database containing broadband frequency block information and trunked radio channel information with the assignment of the broadband frequency block.
20. A method of for managing resources in a multi bearer wireless communication system having a trunked radio system and a broadband data system including:
- receiving a request for a radio call or a data connection by a terminal in the multi bearer system,
- reading availability of radio channels which could be used by the terminal in the trunked radio system,
- reading availability of frequency blocks which could be used by the terminal in the broadband data system,
- reviewing policies relating to use of bearers in the multi bearer wireless communication system, and
- establishing the radio call or data connection according to the policies and the availability of radio channels or frequency blocks.
21. A method according to claim 20 further including:
- determining that the request relates to an emergency call,
- determining that no existing radio channels are available for the call using the trunked radio system,
- determining a radio channel in an available frequency block of the broadband data system, and
- establishing the emergency call using the radio channel.
22. A method according to claim 20 wherein the policies relate to one or more of:
- reduction of interference between active trunked radio channels and active broadband frequency blocks,
- preference of bearer according to emergency status of a call,
- preference for mode of trunked radio operation in relation to active broadband frequency blocks, or
- preference of bearer according to signal strength or signal quality.
Type: Application
Filed: Nov 8, 2016
Publication Date: Feb 23, 2017
Inventor: Clive Douglas HORN (Christchurch)
Application Number: 15/346,518