Patent Application
20070147487
The exemplary and non-limiting embodiments of this invention relate generally to wireless communications systems and, more specifically, relate to the transmission of an information stream to a receiver.
The following abbreviations are herewith defined:
The so-called evolved UTRAN (E-UTRAN) is currently a study item within the 3GPP. For the E-UTRAN system OFDM has been selected as the multiple access scheme for the downlink (i.e., in the direction from the BS to the UE).
In order to obtain maximum flexibility and also increase the potential peak data rate, one approach is to allocate the full system bandwidth at all cells in the system (thus setting the frequency reuse factor to 1/1). However, this approach creates the potential for a problem to occur at cell edges, where the interference from other cells may be so strong that reception is not possible at all.
Reference may be had to 3GPP, “Physical Layer Aspects for Evolved UTRA”, TR 25.814, v 1.0.1 (2005-11). For example, section 7.1.2.6 is directed to downlink inter-cell interference mitigation.
The concept of using per sub-carrier modulation for optimum performance has been noted (especially when considering frequency domain link adaptation), but it is a complex task to also transmit the modulation scheme information for all sub-carriers. Reference in this regard may be had to “A Blockwise Loading Algorithm for the Adaptive Modulation Technique in OFDM Systems”, Grunheid, R.; Bolinth, E.; Rohling, H., Vehicular Technology Conference, 2001, VTC 2001 Fall EEE VTS 54th, Vol. 2, 7-11 Oct. 2001, pages 948-951, vol. 2.
Reference may also be had to “Bit and Subcarrier Allocation for OFDM Transmission Using Adaptive Modulation”, Chu, H; An, C.; Proceedings of the 7th Korea-Russia International Symposium, KORUS 2003, pages 82-85. These authors propose changing the channel modulation scheme according to estimated channel state information.
A first embodiment of the invention is a method comprising: dividing system bandwidth in a wireless communication system into a plurality of sub-bands; using at least two sub-bands of the plurality for transmitting signals in a particular cell of the wireless communication system; allocating signal transmission power for use in transmitting signals in each of the sub-bands in use in the particular cell in accordance with a power sequence; selecting modulation schemes for transmitting signals in each of the sub-bands in use in the particular cell in dependence on signal transmission power allocated to each of the sub-bands in use in the particular cell; and transmitting signals in the sub-bands of the particular cell in accordance with the power sequence and selected modulation schemes.
A second embodiment of the invention is a user equipment comprising: a memory storing a program configured to control the user equipment when executed; a transceiver configured for bidirectional communication across a plurality of sub-bands in a cellular wireless communications system; a data processor coupled to the memory and transceiver, the data processor configured to execute the program and to control the user equipment; and wherein the transceiver is further configured to receive a plurality of signals transmitted in a plurality of sub-bands within a particular cell of the cellular wireless communications system, wherein each signal transmitted in a particular sub-band is both transmitted in accordance with a power sequence, wherein the power sequence assigns a signal transmission power level to at least one of the sub-bands that is different from the signal transmission power levels assigned to other sub-bands; and modulated using a modulation scheme selected in dependence on the signal transmission power level allocated to the sub-band.
A third embodiment of the invention is a base station comprising: a memory storing a program configured to control the base station when executed; a transceiver configured for bidirectional communication across a plurality of sub-bands in a cellular wireless communications system; a data processor coupled to the memory and transceiver, the data transceiver configured to execute the program and to control the base station; and wherein the transceiver is further configured to transmit a plurality of signals in a plurality of sub-bands of a particular cell in a cellular wireless communications system, wherein each signal transmitted in a particular sub-band is both transmitted in accordance with a power sequence, where the power sequence assigns a signal transmission power level to at least one of the sub-bands that is different from the signal transmission power levels that are assigned to other sub-bands; and modulated using a modulation scheme selected in dependence on the signal transmission power level assigned to the particular sub-band.
A fourth embodiment of the invention comprises a computer program product comprising a computer readable memory medium tangibly embodying a computer readable program, the computer readable program executable by data processing apparatus, the computer readable program, when executed by data processing apparatus, configured to divide system bandwidth in a wireless communication system into a plurality of sub-bands; to use at least two sub-bands of the plurality for transmitting signals in a particular cell of the wireless communication system; to allocate signal transmission power for use in transmitting signals in each of the sub-bands in use in the particular cell in accordance with a power sequence; to select modulation schemes for transmitting signals in each of the sub-bands in use in the particular cell in dependence on signal transmission power allocated to each of the sub-bands in use in the particular cell; and to transmit signals in the sub-bands of the particular cell in accordance with the power sequence and selected modulation schemes.
A fifth embodiment of the invention comprises a computer program product comprising a computer readable memory medium tangibly embodying a computer readable program, the computer readable program executable by data processing apparatus, the computer readable program, when executed, configured to receive a signal indicating signal transmission power levels used in transmitting at least first and second signals in at least first and second sub-bands in a particular cell of a cellular wireless communications system; to determine the modulation schemes used to modulate the first and second signals in dependence on the signal indicating the signal transmission power levels used to transmit the first and second signals; and to demodulate the signals in accordance with the determined modulation schemes.
In the attached Drawing Figures:
One possible approach to circumvent the interference problem discussed above is to use a method that can be referred to as power sequencing in the time or frequency domain. From a network planning/coordination point of view, the power sequence method in the frequency domain is the most attractive. The power sequences would be typically employed such that the total system bandwidth is divided into three equal-sized sub-bands which have different transmit power levels allocated for different cells/sectors. Simulations have shown that good performance is obtained where one sub-band is transmitted at a certain power level, while the other two sub-bands are transmitted at power levels that are different from the power level of the strongest sub-band. As a non-limiting example, the other two sub-bands may be transmitted at power levels that are approximately 4 dB lower than the power level of the strongest sub-band.
However, consider a case where the power sequencing method is applied, and also where a user is to be scheduled over the full system bandwidth, or where a user may be scheduled resources simultaneously in a high power and a low power part of the spectrum, while perhaps not over the full system bandwidth. It can be shown that this scenario will cause some bits/symbols to be transmitted (and thus also received) with a higher power than others, thereby resulting in a higher received SINR value for these transmitted bits/symbols.
It has been realized that the sub-band to sub-band power difference of 4 dB is approximately equal to the SINR difference between different modulation schemes. That is, the difference in SINR to achieve a certain bit error rate (BER) between QPSK and 16-QAM is approximately 4-5 dB, and the SINR difference between 16-QAM and 64-QAM is also approximately 4-5 dB. This SINR difference between modulation schemes is thus exploited for data rate optimization by selecting an appropriate modulation scheme for the different sub-bands.
Reference is made first to
In general, the various embodiments of the UE 110 can include, but are not limited to, cellular telephones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.
The embodiments of this invention may be implemented by computer software executable by the data processor 112 of the UE 110 and the other data processors, or by hardware, or by a combination of software and hardware.
The memories 114, 124 and 144 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors 112, 122 and 142 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.
In accordance with exemplary embodiments of this invention, by making the allocated modulation scheme a function of the power allocated for each sub-band, the detection by the UE 110 of the applicable modulation scheme becomes relatively simple and straight-forward.
The exemplary embodiments of this invention use a plurality of modulation schemes over the system bandwidth for a message transmitted to a single UE 110 over multiple sub-bands that use a power sequence for interference reduction.
In accordance with the exemplary embodiments of this invention there is provided a maximum gap of one modulation order:
(QPSK - - - 16-QAM, or 16-QAM - - - 64-QAM)
for each transmission.
In one exemplary and non-limiting embodiment the power sequences applied by the Node B 120 in the frequency domain are standardized. At a minimum, the bands on which power sequences are used are known to the UEs 110. In this situation one of the following three cases is assumed to exist, either: a) power sequences with sufficient power differences are always used in all cells, b) it is signaled to the UE 110 that power sequences with sufficient power difference are used in a particular cell, c) or the UE 110 detects whether a power sequence with at least a threshold amount of power difference is in use (note that if one assumes that the UE 110 has knowledge of the bundled frequency resources, the detection can be performed with some reliability). For this purpose it is preferred that a standardized step in the power sequences exist, for example, differences smaller than about 3 dB would not be permitted by the applicable specification(s).
If one of the three cases (a), (b) or (c) is realized, it follows that if the AMC level is signaled to be QPSK, then the UE 110 can assume that QPSK is used on the low power regime, and 16-QAM on the high power regime (or vice versa, if the AMC is signaled to be 16-QAM, then QPSK is used on the low power regime), with a similar reduction in the AMC signaling.
This technique reduces signaling overhead due to bit loading in the frequency domain, and enhances gain.
It can be noted that it is desirable that there be some common knowledge between the UE 110 and the Node B 120 in order to reduce the amount of signaling between these two units.
The advantages realized by the use of the exemplary embodiments of this invention are several. In one aspect the data rate is potentially increased by permitting the use of a higher order modulation on the high power sub-band (e.g., there can exist a 33% potential increase in peak throughput for the QPSK+16-QAM case), although in practice the actual increase may be less since the additional power may potentially also have been used to decrease the coding, thus also increasing the data rate. A more conservative estimate of the potential throughput increase is approximately 10%.
In another aspect, all of the bits for detection are provided with approximately the same average received SINR (excluding channel variations), thus leading to enhanced performance of the forward error correction scheme that is in use. With the described embodiments of this invention, these performance/throughput improvements can be achieved without increasing the AMC signaling overhead.
In a further non-limiting aspect of the invention, AMC is applied in the setting of a multi-antenna transmission. So called multiple-input multiple-output (MIMO) methods increase the data rate by adding the possibility to transmit multiple signal streams simultaneously to a user. Thus the AMC can be extended to operate, in addition to the modulation and coding domain, in the domain of the number of streams which all characterize a MIMO transmission method. In this aspect of the invention, there is a predefined connection between a MIMO transmission method applied on a low-power resource, and a MIMO transmission method applied on a high-power resource. Thus only one of these needs to be signaled. Note that the predefined connection may be limited to the part of the definition of a MIMO transmission scheme that relates to the data rate (i.e. code rate, modulation order, number of streams). In addition to these, data related to the channel realizations on the individual resource units, such as beam information, may or may not be used to determine a MIMO transmission.
Based on the foregoing it should be apparent that the exemplary embodiments of this invention provide a method, apparatus and computer program product(s) to selectively demodulate received signals as a function of the power level of various sub-bands in which the signals are received, where different modulation schemes are applied at a transmitter so as to substantially equalize at the receiver the received SINR of the signals in the various sub-bands.
In a typical embodiment of the method depicted in
When performing step 530, signal transmission power is allocated in such a manner so as to mitigate signal interference with adjacent cells transmitting in at least some of the same sub-bands.
During typical operation of the method depicted in
In variants of the method depicted in
In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.
Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.
Programs, such as those provided by Synopsys, Inc. of Mountain View, Calif. and Cadence Design, of San Jose, Calif. automatically route conductors and locate components on a semiconductor chip using well established rules of design as well as libraries of pre-stored design modules. Once the design for a semiconductor circuit has been completed, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility or “fab” for fabrication.
Various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. For example, while the exemplary embodiments of the invention have been described above in the context of the UTRAN and E-UTRAN systems, it should be appreciated that the exemplary embodiments of this invention can be applied as well to other types of wireless communications systems, methods and schemes. Further by example, in other embodiments more or less than three sub-bands may be employed, as may different types of modulation schemes. However, any and all modifications of the teachings of this invention will still fall within the scope of the non-limiting embodiments of this invention.
Furthermore, some of the features of the various non-limiting embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.
Priority is herewith claimed under 35 U.S.C. § 119(e) from co-pending Provisional Patent Application 60/754,440, filed on Dec. 27, 2005 by Frank Frederiksen, Preben Mogensen, Troels Kolding, Olav Tirkkonen and Klaus Hugl entitled “APPARATUS, METHOD AND COMPUTER PROGRAM PRODUCT PROVIDING DYNAMIC MODULATION SETTING COMBINED WITH POWER SEQUENCES”. The disclosure of this Provisional Patent Application is hereby incorporated by reference in its entirety as if fully restated herein.
| Number | Date | Country | |
|---|---|---|---|
| 60754440 | Dec 2005 | US |
