WO2015139741A1

WO2015139741A1 - Dynamic radio resource management

Info

Publication number: WO2015139741A1
Application number: PCT/EP2014/055459
Authority: WO
Inventors: Martin HESSLER; Fredrik Lindqvist
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-03-18
Filing date: 2014-03-18
Publication date: 2015-09-24

Abstract

The present disclosure relates to dynamic radio resource management performed in a network node in a wireless network for dynamically configuring a radio link for transmission to/from the network node. The disclosure presents a method embodiment performed in a network node in a wireless network, of configuring a radio link for transmission to/from the network node. The method comprises determining (S1) in the network node at least one hardware specific maximum output power limit for transmission on the radio link, each maximum output power limit corresponding to a respective modulation and coding scheme, MCS. The network node selects (S2) an MCS for transmission on the radio link and configures (S3) an output power for a radio link transmission based on the hardware specific maximum output power limit and selected MCS.

Description

Dynamic radio resource management TECHNICAL FIELD

The present disclosure relates to dynamic radio resource management performed in a network node in a wireless network for dynamically configuring a radio link for

transmission to/from the network node.

BACKGROUND

3GPP Long Term Evolution, LTE, is the fourth-generation mobile communication technologies standard developed within the 3rd Generation Partnership Project, 3GPP, to improve the Universal Mobile Telecommunication System, UMTS, standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. In a typical cellular radio system, wireless devices or terminals also known as mobile stations and/or user equipment units, UEs, communicate via a radio access network, RAN, to one or more core networks. The Universal Terrestrial Radio Access Network, UTRAN, is the radio access network of a UMTS and Evolved UTRAN, E-UTRAN, is the radio access network of an LTE system. In an UTRAN and an E- UTRAN, a User Equipment, UE, is wirelessly connected to a Radio Base Station, RBS, commonly referred to as a NodeB, NB, in UMTS, and as an evolved NodeB, eNB or eNodeB, in LTE. An RBS is a general term for a radio network node capable of transmitting radio signals to a UE and receiving signals transmitted by a UE. Radio resource management, RRM, techniques are implemented to manage the radio resources, e.g. spectra, used for the communication in the network and to provide spectral efficiency. Dynamic RRM techniques such as scheduling and link adaption provide the ability to adjust radio resource use according to traffic load, quality, path loss and interference, among other characteristics. Scheduling and link adaptation, play a central role for resource allocation and have a significant influence on system performance. The scheduling allocates a certain part of a spectrum, i.e. of the available frequency resources, to a certain UE during a certain amount of time. In LTE, no dedicated data channels are used; instead, shared channel resources are used in both downlink and uplink. These shared resources, the Physical Downlink Shared Channel, PDSCH, and the Physical Uplink Shared Channel, PUSCH, are each controlled by one or more schedulers that assign(s) different parts of the downlink and uplink shared channels to different UEs for reception and transmission, respectively. The link adaptation determines the appropriate modulation and level of error correction coding that should be given operating channel conditions, a transmit power and a desired probability of a correct reception. Link adaptation can for example be accomplished by changing the modulation and/or channel coding scheme, MCS. Selection of an appropriate MCS allows the wireless communication network to efficiently utilize the spectrum according to wireless communication characteristics. A main operating principle in conventional scheduling and link adaption is to transmit as much data bits as possible given a certain frequency resource allocation. With conventional link adaptation, an MCS of highest order is chosen for each transmission. However, the highest order of MCS typically requires a high SIN R. With a high SI NR requirement, more power needs to be transmitted/received in order to reach a satisfactory performance for a given channel quality. In a wireless communication system, such as LTE, power control is applied for uplink physical channels. The aim for the uplink power control is to maintain a target received power at the receiving radio base station, RBS, e.g. eNodeB. The power control is commonly designed to optimize the operation for a number of UEs for which the path-gain can differ a lot. The power control mechanism is designed to increase the power for a transmitting wireless device with low path-gain, striving for an equal power density in frequency domain, i.e. W/Hz, in order to maintain good performance. An increase of the frequency resource assignment also im plies an increase in UE output power. For the uplink data channel PUSCH, the transmitted power by a U E in a subframe i, in a cell j, is determined by: P_pusc_H( = min{P_c^,101og₁₀(M_PUSCH(i)) + P_{O PUSCH}(j) + a(j) - PL + A_TF(i) + f(i)}

Where PCMAX is the configured maximum UE transmit power, M _USCH (0 is the number of resource blocks allocated for the UE, PO_PUSCHO) is a parameter consisting of the sum of a cell-specific and a UE-specific part provided by higher layer, a is a cell-specific parameter configured by higher layers (also known as fractional pathloss compensation factor), PL is the downlink pathloss estimate calculated in the UE, Δ_ΤΡ(ί) is a UE-specific parameter provided by higher layers and f(i) is a UE-specific correction term controlled by TPC commands sent in uplink grants sent on the PDCCH. For later releases of the 3GPP specifications the power control, as defined in the specifications, is more complicated due to the support of multi-carrier where UE can support multiple serving cells. The base station has thus several parameters to tune according to a desired power control principle. In state of the art solutions several such power control principles can be found. The power control algorithms target a heterogeneous network consisting of high- power nodes (macro) and lower-power nodes (micro/pico). In a heterogeneous network, power-imbalance between the nodes may result in a pathloss to a neighbor non-serving node being lower than a pathloss to the serving node. This means that a UE connected to a high-power node may cause high interference in a neighbor lower-power cell when attempting to maintain a target received power to its serving node.

In emerging network deployments, very small cells are formed around pico radio base stations, picoRBS, that are introduced to increase capacity and performance. The picoRBSs are often deployed to meet high traffic demands and give users access to high bitrates. UEs in the small cells usually get very good path-gain but also better other channel properties, i.e. line of sight with a very flat stationary channel. The power control and link adaptation algorithms are mostly designed to handle bad situations with poor path-gain and tricky multi-path channels and are designed under the assumption that there is a direct correlation between increased performance and an increase of power. However, there are also situations where use of the current power control and link adaptation algorithms provide exactly the opposite result, i.e. that an increase of power on the uplink, e.g. on the uplink data channel PUSCH, results in a performance degradation. Such performance degradation in response to increased power not only affects the UE that then operates with incorrect power and frequency allocation, but also other UEs in the system that will experience higher interference and a deficit of frequency resources. SUMMARY

It is an object of the present disclosure to provide embodiments solving the problem of dynamic radio resource management in network deployments experiencing problems caused by high as well as low SINR. In particular, it is an object of the disclosure to provide embodiments for dynamic radio resource management suitable in small cell settings and taking an effect from hardware impairments on radio link performance into account.

This object is achieved by a method performed in a network node, a network node configured to perform the method and a computer program run in the network node. The disclosure presents a method embodiment performed in a network node in a wireless network, of configuring a radio link for transmission to/from the network node. The method comprises determining in the network node at least one hardware specific maximum output power limit for transmission on the radio link, each maximum output power limit corresponding to a respective modulation and coding scheme, MCS. The network node selects an MCS for transmission on the radio link and configures an output power for a radio link transmission based on the hardware specific maximum output power limit and selected MCS.

The disclosed method improves coverage and wireless device performance in a wireless network by considering hardware impairments of the radio link as well as the power budget when configuring an output power of the link. The disclosure addresses new use cases with higher SINR and coverage limited scenarios and enables increased spectrum efficiency in the wireless network.

According to an aspect of the disclosure, the network node is a radio access node of the wireless network. According to a further aspect of the disclosure, the network node is a low power radio base station in a 3GPPP wireless network. According to an aspect of the disclosure, the network node is a wireless device having a direct wireless link to another wireless device for device to device communication.

Thus, the disclosed method is generally applicable to configuration of a communication link in the wireless interface of a wireless network, e.g. a link between a wireless device, e.g. user equipment, UE, or a machine device, MD, and a radio base station, e.g. an eNB or a picoRBS, or a communication link between two wireless devices communicating in a device to device deployment.

According to an aspect of the disclosure, the configured output power is configured for a transmission in a subframe on an uplink physical channel from a wireless device, or configured for transmission in a subframe on a downlink physical channel to a wireless device.

According to an aspect of the disclosure, the configured output power is configured for transmission on a backhaul radio link to/from a backhaul hub in the wireless network.

According to an aspect of the disclosure, the hardware specific maximum output power limit for an MCS is determined by estimating a hardware impairment impact on radio link performance for a respective MCS.

According to an aspect of the disclosure, the hardware impairment impact estimate for an MCS is an EVM, Error Vector Magnitude estimate of radio link performance for the MCS. Consideration of an impairment measure impact, e.g. the EVM impact on radio link performance for a specific MCS, enables improved tuning of parameters as part of power control.

According to an aspect of the disclosure, the impairment measure impact on radio link performance for a specific MCS is estimated by iteratively altering output power for transmission on the radio link and determining the hardware specific maximum output power limit as a power level where a performance measure starts to deteriorate with increasing power for the selected MCS. According to an aspect of the disclosure, the radio link performance is determined as a signal to interference plus noise ratio, SINR.

According to an aspect of the disclosure, the hardware specific maximum output power limit is determined from a predetermined set of values, each value representing a hardware specific maximum output power limit for a specific MCS.

According to an aspect of the disclosure, the predetermined set of values represents a specific type, category or model of wireless device.

According to an aspect of the disclosure, the method further includes receiving one or more values representing respective hardware specific output power limits from the wireless device and determining the hardware specific maximum output power limit based on the values received from the wireless device.

According to an aspect of the disclosure, the disclosed method further includes the step of initiating transmission with selected MCS at the configured output power.

According to an aspect of the disclosure, the disclosed method further includes the step of determining radio link performance for transmission performed with selected MCS and configured output power.

According to an aspect of the disclosure, the hardware specific maximum output power limit is updated based on the determined radio link performance.

According to an aspect of the disclosure, the disclosed method further includes the step of reducing the configured output power and repeating the steps of initiating radio link transmission at the configured output power and selected MCS and determining radio link performance when the EVM exceeds a predetermined threshold.

The disclosure also relates to a network node arranged to configure a radio link for transmission to/from the network node. The network node comprises a processor, a wireless communication interface for transmission to/from the network node, and a memory, said memory containing instructions executable by said processor. The network node is operative to determine for at least one modulation and coding scheme, MCS, a hardware specific maximum output power limit for transmission on the radio link; select a modulation and coding scheme, MCS, for transmission on the radio link; and configure an output power for a radio link transmission based on the hardware specific maximum output power limit and selected MCS. According to an aspect of the disclosure, the memory is further configured to store predetermined set of values, each value representing a predetermined hardware specific maximum output power limit for a specific MCS.

According to an aspect of the disclosure, the network node is further operative to initiate uplink or downlink transmission with selected MCS at the configured output power. According to an aspect of the disclosure, the network node is further operative to determine radio link performance for a selected MCS and configured output power, and to determine a hardware specific maximum output power limit for transmission on the radio link with the selected MCS.

The disclosure also relates to a computer-readable storage medium, having stored there on a computer program which when run in a network node, causes the network node to perform the disclosed method.

The network node and the computer-readable storage medium each display advantages corresponding to the advantages already described in relation to the disclosure of the method in a network node. BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages of the present disclosure will appear from the following detailed description, wherein some aspects of the disclosure will be described in more detail with reference to the accompanying drawings, in which:

Figure 1 a. shows the basic LTE architecture b. discloses a cellular structure with pico radio base stations Figure 2 discloses an example block diagram of a transmitter-receiver chain illustrating radio impairments

Figure 3 a. discloses throughput versus error vector magnitude, EVM, for MCS in LTE uplink b. discloses throughput versus output power at high SINR for MCS

Figure 4 is a flowchart schematically illustrating embodiments of method steps performed in a network node

Figure 5 is block diagram schematically illustrating a network node embodiment DETAILED DESCRIPTION

The general object or idea of embodiments of the present disclosure is to address at least one or some of the disadvantages with the prior art solutions described above as well as below. The various steps described below in connection with the figures should be primarily understood in a logical sense, while each step may involve the communication of one or more specific messages depending on the implementation and protocols used.

Embodiments of the present disclosure relate, in general, to the field of dynamic radio resource management in network deployments experiencing problems caused by high as well as low SINR. In particular, the disclosure relates to dynamic radio resource management in an access node taking the effect from hardware impairments on radio link performance into account.

Figure la schematically illustrates a basic LTE, Long Term Evolution, network architecture, including radio base stations, RBS, arranged for communicating with wireless devices over a wireless communication interface. The plurality of RBSs, here shown as eNBs, is connected to MME/S-GW entities via SI interfaces. The eNBs are connected to each other via X2 interfaces. Figure lb exemplifies a network deployment wherein very large capacity and performance is sought by deploying small cells 210 defined by the coverage areas of low power radio base stations 21, RBSs, in the following denominated picoRBSs. A macro radio base station 20, e.g. eNB, provides coverage in a large cell 200 including a number of small cells 210. The picoRBSs 21 are typically geographically oriented to densely populated areas with many users in the vicinity of a picoRBS. A wireless device 10, e.g. a mobile/cellular phone or any other type of user equipment, is using a Radio Access Network, RAN, service to access the mobile network services. The picoRBS may provide one or a combination of several radio access technologies over the radio access link, e.g. 3GPP LTE, 3GPP HSPA, 3GPP GSM or IEEE 802.11x, also known as Wi-Fi. The PicoRBS needs to backhaul the RAN traffic to the mobile network, and uses a wireless backhaul link for this.

Due to the closeness resulting from the heterogeneous network, a wireless device 10 in the network is experiences very good path-gain but also better other channel properties, i.e. line of sight with a very flat stationary channel. In the heterogeneous deployment, some small cells could also be situated indoor, which implies that the interference level can also be low for wireless devices in small cells. Typically, a high SINR is common in this setting.

Wireless devices in the heterogeneous cell is the same wireless devices that can be situated in other situations, for example, on a train with very high and tricky fast fading channel, or in a rural area with very poor path-gain. This implies that the power control and link adaptation needs to be flexible enough to handle both these situations.

Figure 2 discloses a block diagram of a transmitter-receiver chain illustrating a radio chain and hardware components affecting the performance of the radio link due hardware impairments. The impact on radio link performance is estimated with known impairment measures such as cubic meter measure or error vector magnitude, EVM, measure. EVM is a measure used to estimate the deviation between transmitted IQ.-symbols, in-phase quadrature-symbols, and demodulated IQ.-symbols, assuming a transmitter-receiver pair in LTE uplink/downlink. In the following disclosure, the discussion on estimation of hardware impairment impacts on radio link performance will be made with reference to EVM. However, other types of impairment measures are naturally within the scope of the disclosure.

Looking at EVM, a root-mean-square (RMS) EVM measure is defined:

Where X_k(n) is a transmitted IQ.-symbol at subcarrier/sample k at the nth transmitted OFDM/SC-FDMA symbol-waveform. M denotes the number of assigned subcarriers for the considered UE. Similarly, E_k(n) denotes the corresponding error between transmitted and received 10-symbol, i.e. the constellation error. Unavoidable hardware impairments, e.g. power-amplifier characteristics, contribute to the overall EVM. Thus, the EVM depends on the specific power amplifier hardware and can be interpreted as a power- dependent performance. The SINR can be estimated from the EVM as

SINR = -201og₁₀(£y _rms[%]/100)

[3]

Unavoidable radio impairments such as phase noise, I -im balance, and nonlinear power- amplifier (PA) characteristics contribute to the overall EVM. Of particular interest is the power-dependent EVM of a typical PA. The power dependency of EVM could be translated to a power-dependent performance. Figure 3a discloses an example of throughput versus error vector magnitude, EVM, for MCS in LTE uplink.

Figure 3b discloses an example of throughput versus output power at high SINR for MCS. The figure exemplifies the effect of radio hardware impairments on the radio link performance, where increasing power increases the EVM and hence lowers an effective SINR. The graph discloses that PCMAX(i,16) is about 5 dB larger than PCMAX(i,28). This is an effect of the current design of power control and link adaptation. The graph discloses that a gain of approximately 5 dB is possible in the link-budget for MCS 16 for the path- gain limited wireless devices when considering an output power limit for using MCS 28. Figure 3b exemplifies the benefits that are possible to achieve from an improved configuration of a radio link taking Figure 4 is a flowchart schematically il lustrating embodiments of method steps performed in a network node to provide for an improved radio link configuration taking hardware impairments into consideration. In the following disclosure, the network node is exemplified with a low power radio access node of a 3GPP wireless network. However, it should be noted that the disclosure is also applicable to other types of radio access nodes of a wireless network, e.g. an eN B of a 3GPPP network. Furthermore, the principles described below are also applicable when configuring radio links for device to device communication, D2D communication, wherein a wireless device has a direct radio link to another wireless device for D2D communication. Thus, the disclosed method is generally applicable to configuration of a communication link in the wireless interface of a wireless network, e.g. a link between a wireless device, e.g. user equipment, UE, or a machine device, MD, and a radio base station, e.g. an eNB or a picoRBS, or a communication link between two wireless devices communicating in a device to device deployment.

In a first step SI at least one hardware specific maximum output power limit P_CMAX(M CS) for transmission on the radio link is determined. In accordance with one aspect applicable to a 3GPP LTE context, a max power setting for each M CS per U E or UE category in the uplink is determined PCMAXO, M CS), wherein the M CS is the modulation and coding scheme of the transmission format for PUSCH transmission. Similarly, this is also possible in the downlink if power control is introduced for the downlink, i.e. PDSCH, where the receiver EVM would potentially need to be known in the base-station. According to an aspect of the disclosure, the hardware specific maximum output power limit PCMAX(M CS) for an M CS is determined by estimating a hardware impairment impact on radio link performance for a respective M CS, e.g. an EVM, Error Vector Magnitude estimate of radio link performance for the MCS. Each determined maximum output power limit P_CMAX( CS) corresponds to a respective modulation and coding scheme, M CS. Figure 3b discloses throughput versus output power at high SI NR for MCS in LTE uplink and visualizes hardware specific maximum output power limit for each MCS, i.e. the output power value where an increase of the power results in decreasing throughput.

According to an aspect of the disclosure, the impairment measure impact on radio link performa nce for a specific M CS is estimated by iteratively altering output power for transmission on the radio link and determining the hardware specific maximum output power limit as a power level where a performance measure starts to deteriorate with increasing power for the selected M CS. I n one example embodiment, the hardware specific maximum output power limit P_CMAX(MCS) is determined for a backhaul link by iteratively altering output power for each M CS and determining the effect on link performance, e.g. throughput.

As mentioned, we can determine the hardware impairment impact on radio link, e.g. EVM impact on the link, by iteratively altering the power and observing the effects on the radio link performance, thereby optimizing the link. One way of changing the power settings is to use power commands. Another way to change power settings is to change the frequency a llocation of the PUSCH transmissions as the power scales with the amount of frequency domain resources. The performance of the link is measured by a performance function, for example, as the spectral efficiency [bits/Hz] or effective SINR. If we have no power dependent EVM, the SINR increases proportionally to the power. However, with power dependent EVM, the effective SIN R, and thus performance, will not necessarily increase proportionally to the power and eventually deteriorate. From this behavior we can estimate a difference in performance and for the power value estimate the corresponding EVM value. The EVM value could also be directly measured by the transceiver. As disclosed in Figure 3b, the iteration is performed per MCS and the radio link performance determined as a signal to interference plus noise ratio, SINR, to determine a best throughput given a power configuration for a specific MCS.

Essentially, the iteration would estimate the performance for some range of power and EVM values, e.g. according to the algorithm disclosed below:

Estimate the value of function f(Power) by transmitting at power Power

While Pstep > Thr Estimate f(Power+Pstep) by transmitting at power Power+Pstep If f(Power) < f(Power+Pstep) Power = Power+Pstep

Else Pstep = - Pstep / 2

End If End While

Hence after the iterations we know within error Thr (i.e. within an error threshold) a maximum output power value P_CMAX( CS) for the MCS. According to another aspect of the disclosure, the hardware specific maximum output power limit is determined from a predetermined set of values, each value representing a hardware specific maximum output power limit for a specific MCS.

The predetermined set of values is derived from a priori information about the power- dependent EVM characteristics for the considered transceiver pair. According to an aspect of the disclosure, the a priori information is based on a specific type, category or model of wireless device, e.g. 3GPP category, base station type, base station mode, UE radio chipset or even the particular U E model . For example, a network operator can pre- measure, or obtain from an equipment vendor, power-dependent EVM values for a transceiver hardware used in the network. When such transceiver type is switched on in the network, it could be identified from the retrieved user subscription information required prior to establishing the communication link. The EVM information could be pre- known from link-level simulations and pre-stored in e.g. a table, or estimated when the equipment is installed.

As part of the uplink scheduling process, the estimated/measured SI NR and pathloss, PL are used to determine a theoretical output power that the wireless device should use in uplink transmissions in order to reach the desired SI NR.

Furthermore, given the determined theoretical output power Px, the expected EVM value, here called EVMx of the transceiver pair can be retrieved by a table look-up from the pre-known/estimated EVM-versus-power relation, where the EVM-versus-power relation also depends on the MCS. Different modulation types typically give different EVM-versus-power characteristics, while different code rates within a modulation type typically give the same EVM-versus-power relation. Furthermore, given a determined EVMx value, the most appropriate code rate for the considered MCSx can be found by a table look-up from the pre-known/estimated throughput-versus-EVM relation, where the latter is by means of an example depicted in previously mentioned Figure 3a. I n this example, it can be seen that for EVM up to 8% MCS28 is preferred but for EVM between 8% and 20% MCS 23 is preferred, and so on. According to an aspect of the disclosure, the method further includes, in step SO, receiving one or more values representing respective hardware specific output power limits from the wireless device, e.g. information or values representing a specific category or model of wireless device. . The network node, receiving the values or information from the wireless device, uses this information to determine hardware specific maximum output power limit based on the values received from the wireless device, e.g. by using a look-up table including information valid for a specific category or model of wireless device.

In a step S2, the network node selects an MCS for transmission on the radio link. The selection of the MCS is performed in order to optimize throughput and is performed according to state-of-the art solutions for data transmission in wireless networks. Typically, a high MCS will be selected when there is a need to transmit a large amount of data.

In step S3, the network node configures an output power for a radio link transmission based on the hardware specific maximum output power limit P_CMAX(M CS) and selected M CS.

According to an aspect of the disclosure, the output power is configured in step S3a for a specific subframe /^' on an uplink physical channel from a wireless device, i.e. P _PUSCH(', MCS), or correspondingly, in step S3b, for a specific subframe /^' on a downlink physical channel, i.e. P_PDSCH(', MCS) to a wireless device. According to another aspect of the disclosure, the configured output power is configured, in step S3c, for transmission on a backhaul radio link to/from a backhaul hub in the wireless network. Each link of the backhaul system is capable of iteratively finding an optimal radio link configuration with respect to hardware radio link impairments and power settings, when performing the disclosed steps for configuring a radio link.

According to an aspect of the disclosure, the disclosed method further includes the step of initiating S4 transmission with selected MCS at the configured output power.

According to an aspect of the disclosure, the disclosed method further includes the step

55 of determining radio link performance for transmission performed with selected MCS and configured output power.

According to an aspect of the disclosure, the hardware specific maximum output power limit is updated based on a determined radio link performance. When a transmission has been performed according to the M CS dependent power configuration, it is possible to estimate SI NR for the data transmission. The SIN R estimates can be reiterated to determine updated hardware specific maximum output power limits, P_CMAX(M CS), per M CS in step Sla.

56 of reducing the configured output power and repeating the steps of initiating radio link transmission at the configured output power and selected MCS and determining radio link performance when the EVM exceeds a predetermined threshold.

Using the disclosed method, a network node configures the power for radio link transmission based on a selected MCS and overcomes the problem of deteriorating radio link performance at high MCS in high SIN R situations.

Figure 5 is a block diagram schematically illustrating a n example embodiment of a network node for performing the method steps embodiments. Figure 5 illustrates a radio access node, e.g. an eN B or a picoRBS configured to perform the method steps. However, the illustration is also applicable to a wireless device configured for device-to-device communication, D2D, to another wireless device. The network node 50 comprises a processor 51 or a processing circuitry that may be constituted by any suitable Central Processing Unit, CPU, microcontroller, Digital Signal Processor, DSP, etc. capable of executing computer program code. The computer program may be stored in a memory, MEM 53. The memory 53 can be any combination of a Random Access Memory, RAM, and a Read Only Memory, ROM. The memory 53 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, or solid state memory or even remotely mounted memory. The network node 50 further comprises a communication interface 52 configured communication with wireless devices in the network.

According to one aspect the disclosure further relates to a computer-readable storage medium, having stored thereon the above mentioned computer program which when run in a network node, causes the node to perform the disclosed method embodiments. When the above mentioned computer program is run in the processor of the network node 50, it causes the node to determine for at least one modulation and coding scheme, MCS, a hardware specific maximum output power limit for transmission on the radio link; select a modulation and coding scheme, MCS, for transmission on the radio link; and configure an output power for a radio link transmission based on the hardware specific maximum output power limit and selected MCS.

According to an aspect of the disclosure, the memory 53 is further configured to store predetermined set of values, each value representing a predetermined hardware specific maximum output power limit for a specific MCS.

According to an aspect of the disclosure, the network node is further operative to initiate uplink or downlink transmission with selected MCS at the configured output power.

According to an aspect of the disclosure, the network node is further operative to determine radio link performance for a selected MCS and configured output power, and to determine a hardware specific maximum output power limit for transmission on the radio link with the selected MCS. The disclosure also relates to a computer-readable storage medium, having stored there on a computer program which when run in a network node, causes the network node to perform the disclosed method.

According to a further aspect of the disclosure, processor 51 further comprises one or several of:

- a determination module 511 configured to determine at least one hardware specific maximum output power limit for transmission on the radio link, each maximum output power limit corresponding to a respective modulation and coding scheme, MCS; - a selection module 512 configured to select a modulation and coding scheme,

M CS, for transmission on the radio link; and

- a radio link configuration module 513 arranged to configure an output power for a radio link based on the hardware specific maximum output power limit PCMAX (M CS) and selected M CS. The determination module 511, the selection module 512 and radio link configuration module 513 are implemented in hardware or in software or in a combination thereof. The modules 511, 512, 513 are according to one aspect implemented as a computer program stored in a memory 53 which run on the processing circuitry 51.

Claims

A method, performed in a network node in a wireless network, of configuring a radio link for transmission to/from the network node, comprising

- determining (SI) in the network node at least one hardware specific maximum output power limit, P_CMAX(M CS), for transmission on the radio link, each maximum output power limit corresponding to a respective modulation and coding scheme, MCS;

- selecting (S2) a modulation and coding scheme, MCS, for transmission on the radio link; and

- configuring (S3) an output power for a radio link transmission based on the hardware specific maximum output power limit PCMAX (MCS) and selected MCS.

The method of claim 1, wherein the network node is a radio access node of the wireless network.

The method of claim 2, wherein the network node is a low power radio base station in a 3GPP wireless network.

The method of claim 1, wherein the network node is a wireless device having a direct wireless link to another wireless device for device to device communication.

The method of any of claims 1 to 4, wherein the configured output power is configured (S3a) for a transmission in a subframe /^' on an uplink physical channel, PPUSCH(') f^{ro m a} wireless device, or configured (S3b) for transmission in a subframe /^' on a downlink physical channel, PPDSCH(') to a wireless device.

The method of any of claim 1-4, wherein the configured output power is configured (S3c) for transmission on a backhaul radio link to/from a backhaul hub in the wireless network. The method of any of claims 1-6, wherein the hardware specific maximum output power limit P_CMAX(M CS) for an MCS is determined by estimating (Sla) a hardware impairment impact on radio link performance for a respective MCS. The method of claim 7, wherein the hardware impairment impact estimate for an

MCS is an EVM, Error Vector Magnitude estimate of radio link performance for the MCS. The method of claim 7 or 8, wherein the impairment measure impact on radio link performance for a specific M CS is estimated by iteratively altering output power for transmission on the radio link and determining the hardware specific maximum output power limit P_CMAX( CS) as a power level where a performance measure starts to deteriorate with increasing power for the selected M CS. The method of any of claims 7-9, wherein the radio link performance is determined as a signal to interference plus noise ratio, SINR. The method of any of claims 1-6, wherein the hardware specific maximum output power limit P_CMAX(M CS) is determined from a predetermined set of values (Sib), each value representing a hardware specific maximum output power limit PCMAX(M CS) for a specific M CS. The method of claim 11, wherein the predetermined set of values represents a specific type, category or model of wireless device. The method of any of the preceding claims, further including receiving (SO) one or more values representing respective hardware specific output power limits from the wireless device and determining (SI) the hardware specific maximum output power limit P_CMAX( CS) based on the values received from the wireless device. The method of any of the preceding claims, further including initiating (S4) transmission with selected MCS at the configured output power. The method of claim 14, further including determining (S5) radio link performance for transmission performed with selected MCS and configured output power. The method of claim 15, wherein the hardware specific maximum output power limit PCMAX(M CS) is updated based on determined radio link performance. The method of claim 15 or 16, further including the step of reducing the configured output power and repeating the steps of initiating (S4) radio link transmission at the configured output power and selected MCS and determining (S5) radio link performance when the EVM exceeds a predetermined threshold. A network node (50) arranged to configure a radio link for transmission to/from the network node, comprising a processor (51), a wireless communication interface 52 for transmission to/from the network node, and a memory 53, said memory containing instructions executable by said processor whereby the network node is operative to:

- determine (SI) for at least one modulation and coding scheme, MCS, a hardware specific maximum output power limit, PCMAX( CS), for transmission on the radio link;

- select (S2) a modulation and coding scheme, M CS, for transmission on the radio link; and

- configure (S3) an output power for a radio link transmission based on the hardware specific maximum output power limit P_CMAX(M CS) and selected M CS. The network node (50) of claim 13, wherein the memory is further configured to store predetermined set of values (Sib), each value representing a predetermined hardware specific maximum output power limit P_CMAX( CS) for a specific M CS. The network node (50) of claim 13 or 14, further operative to initiate uplink or downlink transmission with selected M CS at the configured output power. The network node (50) of claim 16, further operative to determine (S5) radio link performance for a selected M CS and configured output power, and to determine a hardware specific maximum output power limit, P_CMAX(M CS) for transmission on the radio link with the selected M CS. A computer-readable storage medium, having stored there on a computer program which when run in a network node, causes the network node to perform the method as claimed in any of claims 1-16.