Patent Application
20090225716
The invention is based on a priority application EP 08 290 214.9 which is hereby incorporated by reference.
The invention relates to a method of link adaptation in a base station and to a computer program product.
Link adaptation, or adaptive modulation and coding (AMC), denotes the selection of the modulation, coding and other signal and protocol parameters according to the conditions on the radio link. The conditions may be related to the interference due signals coming from other transmitters, the sensitivity of the receiver, or the available transmitter power margin. Wireless communication standards as e.g. WiMax and LTE use a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) according to the quality of the radio channel, and thus the bit rate and robustness of data transmission. The process of link adaptation is dynamic and the signal and protocol parameters change as the radio link conditions.
Adaptive modulation systems require channel information at the transmitter. This could be acquired, for example, by assuming that the channel from the transmitter to the receiver is approximately the same as the channel from the receiver to the transmitter. Alternatively, the channel information can also be directly measured at the receiver, and sent back to the transmitter. Adaptive modulation systems improve rate of transmission, and bit error rates, by exploiting the channel information that is present at the transmitter. Especially over fading channels which model wireless propagation environments, adaptive modulation systems shows great performance enhancements compared to systems that do not exploit channel knowledge at the transmitter.
There is therefore a need for an improved method of selecting the link adaptation characteristics in a base station, to a base station and to a computer program product to perform the method in accordance with the invention.
The invention relates to a method of selecting link adaptation characteristics in a base station of an OFDM mobile digital communication, the base station being coupled to at least one mobile station, the method comprising the steps of: measuring a mobile station's velocity in the mobile station; receiving a mobile station's velocity value from the mobile station by the base station; calculating a channel estimation and equalization with a first algorithm by the base station, if the mobile station's velocity value is smaller than a first threshold; activating a MIMO Matrix B including spatial multiplexing and activating an AMC permutation mode by the base station, if the mobile station's velocity value is smaller than the first threshold, and if the mobile station occupies multiple antennas; activating a beamforming algorithm and activating the AMC permutation mode by the base station, if the mobile station's velocity value is smaller than the first threshold, and if the mobile station does not occupy multiple antennas.
The method further comprises the steps of: activating a RX/TX diversity algorithm and activating a PUSC permutation mode by the base station, if the mobile station's velocity value is bigger than the first threshold, and if the mobile station does not occupy multiple antennas; activating the MIMO Matrix B including spatial multiplexing and activating the PUSC permutation mode by the base station, if the mobile station's velocity value is bigger than the first threshold, if the mobile station occupies multiple antennas, and if the mobile station's velocity value is smaller than a second threshold; activating a MIMO Matrix A including space time block coding and activating the PUSC permutation mode by the base station, if the mobile station's velocity value is bigger than the first threshold, if the mobile station occupies multiple antennas, and if the mobile station's velocity value is bigger than the second threshold.
The main advantage of the embodiments is that the velocity of the mobile station's is measured by the base station, the value of the measurement is sent to the base station and therefore available immediate for further processing. This may include estimating the right channel estimation and equalization algorithms, the permutation mode to use, or the suitable MIMO matrix. In contrast to all other measurements, as e.g. the CINR variance, require several frame lengths in calculations before they are available as an input.
In accordance with an embodiment, the method further comprises the steps of: calculating the channel estimation and equalization using a second algorithm by the base station, if the mobile station's velocity value is bigger than the first threshold and if the mobile station's velocity value is smaller than the second threshold, wherein the second algorithm provides more accurate channel estimation for this velocity range than the first algorithm, wherein the second threshold is bigger than the first threshold; calculating the channel estimation and equalization using a third algorithm by the base station, if the mobile station's velocity value is bigger than the second threshold, and if the mobile station's velocity value is smaller than a third threshold, wherein the third algorithm provides more accurate channel estimation for this velocity range than the second algorithm, wherein the third threshold is bigger than the second threshold; and calculating the channel estimation and equalization using a fourth algorithm by the base station, if the mobile station's velocity value is bigger than the third threshold, wherein the fourth algorithm provides more accurate channel estimation for this velocity range than the third algorithm. The main advantage of the embodiments is that different algorithms are proposed according to the velocity range of the mobile station, each one of the algorithms providing the most accurate channel estimation for that velocity range.
In accordance with further embodiments, the mobile station's velocity value is sent through an extended fast feedback channel, as e.g. the Channel Quality Indicator Channel (CQICH), to the base station. Alternatively, the mobile station's velocity value is sent with a MAC management message to the base station.
The method as in any of the preceding embodiments, wherein the mobile station's velocity is measured with a Global Positioning System (e.g. GPS, Galileo, Glonass) or motion detection sensors located in the mobile station.
In another aspect, the invention relates to a base station in an OFDM mobile digital communication, the base station coupled to at least one mobile station, the base station comprising: means for receiving a mobile station's velocity value measured by the mobile station; means for calculating a channel estimation and equalization with a first algorithm, if the mobile station's velocity value is smaller than a first threshold; means for activating a MIMO Matrix B including spatial multiplexing and activating an AMC permutation mode, if the mobile station's velocity value is smaller than the first threshold, and if the mobile station occupies multiple antennas; and means for activating a beamforming algorithm and activating the AMC permutation mode, if the mobile station's velocity value is smaller than the first threshold, and if the mobile station does not occupy multiple antennas.
The base station further comprises means for activating a RX/TX diversity algorithm and activating a PUSC permutation mode, if the mobile station's velocity value is bigger than the first threshold, and if the mobile station does not occupy multiple antennas; means for activating the MIMO Matrix B including spatial multiplexing and activating the PUSC permutation mode, if the mobile station's velocity value is bigger than the first threshold, if the mobile station occupies multiple antennas, and if the mobile station's velocity value is smaller than a second threshold; means for activating a MIMO Matrix A including space time block coding and activating the PUSC permutation mode, if the mobile station's velocity value is bigger than the first threshold, if the mobile station occupies multiple antennas, and if the mobile station's velocity value is bigger than the second threshold.
The base station of the embodiments further comprises: means for calculating the channel estimation and equalization using a second algorithm, if the mobile station's velocity value is bigger than the first threshold and if the mobile station's velocity value is smaller than the second threshold, wherein the second algorithm provides more accurate channel estimation for this velocity range than the first algorithm, wherein the second threshold is bigger than the first threshold.
The base station of the embodiments, wherein the mobile station's velocity value is sent with an extended fast feedback channel.
In another aspect, the invention relates to a computer program product stored on a computer usable medium, comprising computer readable program means for causing a computer to perform a method according to any of the embodiments when the program is run on the computer.
In the following preferred embodiments of the invention will be described in greater detail by way of example only making reference to the drawings in which:
After the step 103, in a further step 105, the mobile station velocity is compared with a first velocity threshold V1, and if the velocity is smaller than the velocity threshold, then a normal communication is carrier out between the mobile and the base station. On the other hand, if the variance or the velocity are bigger that its respective thresholds, the algorithm uses a specific channel estimation calculation using the mobile station's velocity and specific burst profile characteristics. This calculation is described in the subsequent figures.
If the mobile station's velocity is larger than the second threshold, the step 205 compares the mobile station's velocity with a third threshold V3. If the mobile station's velocity is smaller than the third threshold, then it indicates that the number of the valid pilots for estimation is even smaller and a third channel estimation and equalization algorithm M3 is applied. This third algorithm M3 provides more accurate channel estimation for this velocity range than the second algorithm M2. If the mobile station's velocity is larger than the third threshold then, in the step 207, a fourth algorithm M4 is applied and the number of valid pilots for estimation is even smaller than the rest of the steps of the calculation. This fourth algorithm M4 uses fewer resources than M3 and it is ideal for the fastest varying channels.
The coding introduces redundancy to protect the original information bits, combating fading, noise and interference. The more redundancy, the better are the information bits protected. Due to the coding, the bit rate after coding is always lower. Modulation and coding are trade-off schemes. They depend on multi-dimensional aspects, such as fading, noise, interference and the signal power. Some of these aspects, as e.g. fading, are strongly influenced by the MS's velocity. It is then possible to use the velocity information as a reference to adaptively choose the best modulation and coding schemes.
On a fourth step 304 of
In a continuation of the burst profile selection of
If the mobile station's velocity is larger than the second threshold, then a sixth step 406 activates a multiple input and multiple output (MIMO) matrix A. The matrix A comprises space time block coding in order to introduce additional high spatial diversity. In the wireless communications as e.g. the WiMAX standard, matrix A is equivalent with Space-Time Block Coding (STBC). It is a one-stream MIMO scheme. The original signal is encoded according to the code matrix (Matrix A), and transmitted via multiple antennas. At the receiver, the spatial redundancy can improve the detection and recover the signal.
If the mobile station's velocity is smaller than the second threshold, then a seventh step 407 uses a MIMO matrix B with spatial multiplexing in order to achieve high throughput over the bandwidth. Matrix B is equivalent with Spatial Multiplexing (SM). It is a multi-stream MIMO scheme. The streams are encoded according to the code matrix (Matrix B), and transmitted via multiple antennas. This scheme has high data rate. The Matrix A and the Matrix B depends on criteria to perform the MIMO switch and in the embodiments, the mobile station's velocity is a key factor. Finally, if the mobile station does not occupy multiple antennas, then an eighth step 408 makes available a reception and transmission diversity algorithm.
The base station 501 further comprises means for activating 507 a RX/TX diversity algorithm and activating a PUSC permutation mode, if the mobile station's velocity value is bigger than the first threshold, and if the mobile station does not occupy multiple antennas; means for activating 508 the MIMO Matrix B including spatial multiplexing and activating the PUSC permutation mode, if the mobile station's velocity value is bigger than the first threshold, if the mobile station occupies multiple antennas, and if the mobile station's velocity value is smaller than a second threshold; and means for activating 509 a MIMO Matrix A including space time block coding and activating the PUSC permutation mode, if the mobile station's velocity value is bigger than the first threshold, if the mobile station uses a, if the mobile station occupies multiple antennas, and if the mobile station's velocity value is bigger than the second threshold.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08 290 214.9 | Mar 2008 | EP | regional |
