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LTE-Advanced Air Interface Technology. FULL ACCESS SubjectsEngineering & Technology. Export Citation DownloadPDF MB. Download LTE-Advanced Air Interface Technology by Xincheng Zhang,Xiaojin Zhou PDF. By Xincheng Zhang,Xiaojin Zhou. Opportunities are handy for execs. Written by experienced researchers and professionals, LTE-Advanced Air Interface Technology thoroughly covers the performance targets and technology .
Turbo Coding Block Interleaving A radio channel produces bursty errors. The purpose of LB is thus to influence the load distribution in such a manner that radio resources remain highly utilized and the QoS of in-progress sessions is maintained to the largest possible extent while call dropping probabilities are kept sufficiently small. Thus, the redundancy version and an indication whether the transmission contains a first transmission or a retransmission is indicated on the PDCCH. LTE provides for each cell 64 such random IDs and thus 64 preambles. The control plane latency should be lower than ms.
Figure shows the different possible antenna configurations. Possible Antenna Configuration The figure also shows the logical antenna mapping, the benefits of this configuration are as follows: The peak throughput could be nearly doubled compared to MIMO schemes which use maximum rank 2 transmission. This is described in Figure below. Carrier aggregation also provides pooling gains across carriers, bringing the effective efficiently of multiple carriers nearly on par with a single carrier having the same bandwidth as the aggregate.
Normally there are some load balancing inefficiencies with multiple independent carriers e. Carrier aggregation can nearly eliminate such inefficiencies. The definition of SCell is just from the UE point of view. The bandwidth combinations that can be aggregated by the Carrier Aggregation feature up to a total of 40MHz are illustrated in Figure above. The feature is also enhanced to support multiple TMs. The following multiple TMs are supported: The transmission mode is TM3. The main benefit of non-contiguous intra-band CA support is to allow the customer to aggregate scattered spectrum in a band as well as allowing spectrum from different bands.
When one or multiple faulty antennas are identified, the cell is setup again automatically with a lower number of antennas degraded mode.
In L14B Carrier aggregation was enhanced from the previous release, and also 2 new optional features were introduced: Note that support for UE category 6 is needed to reach the peak throughput. Dynamic activation and deactivation ensures that the SCell is activated only when there is downlink data demand that could benefit from transmitting on more than just one carrier.
Furthermore the activated secondary cell is used for downlink transmissions only if the SCell downlink channel quality is above a certain threshold based on the reported CQI from the UE. The SCell can only be activated if the number of connected users is below a defined threshold as illustrated in Figure SCell deactivated if: This timer is set with an Ericsson Internal parameter in L13B release, the default value is set to ms.
The UE mobility is handled as existing legacy functionality. PCell always changes due to handover. This is described in Figure Carrier aggregation CA technology is becoming widespread as it addresses both end-user and network capacity aspects UEs with carrier aggregation capability are not always camping on the most appropriate cell from a CA perspective. The feature is divided into two main functional parts: There are three additional parts that are part of the feature scope: If a better cell from a CA perspective is found check based on capacity then an attempt is made to redirect i.
It is a completely separate thing that CATR is rather aggressive in its nature, thereby being allowed to overload the target cell slightly. The fraction of UEs capable of, configured for, activated for and scheduled for CA are also affected.
It will increasingly become mandatory to support carrier aggregation for TDD as part of any operator deployment. Carrier Aggregation CA is used to increase the bandwidth by combining several carriers, and thereby increase the peak bitrates. The limitations are: The DFT size M, i.
Finally, a cyclic prefix is inserted. In the figure we can also see how two different users are assigned different carrier frequencies and bandwidths. This makes the uplink orthogonal. Furthermore, similar to OFDM, the DFTS-OFDM physical resource can be seen as a time-frequency grid with the additional constraint that a resource assigned to a mobile terminal must always consist of a set of consecutive subcarriers in order to keep the single-carrier property of the uplink transmission.
Similar to the downlink the LTE physical-layer specification for the uplink also allows for a very high degree of flexibility in terms of the overall transmission bandwidth by allowing for, in essence, any number of uplink resource blocks. However, once again there will be restrictions in the sense that, at least initially, there will only be radio-frequency requirements defined for a limited set of uplink bandwidths. Furthermore, in order to limit the complexity of the DFT operation, the uplink resource assignment should always be such that the DFT size can always be factorized into factors of 2, 3, and 5.
As the resource-block size itself can be factorized into these factors, this means UL that also the number of assigned resource blocks N RB can be factorized into factors of 2, 3, and 5. As an example, a UE can thus be dynamically assigned an instantaneous bandwidth corresponding to e. Also in terms of the more detailed time-domain structure the LTE uplink is very similar to the downlink. Also similar to the downlink, two cyclic-prefix lengths, a normal cyclic prefix and an extended cyclic prefix are defined for the uplink.
At the same time, uplink scheduling is carried out on a sub-frame 1 ms basis. Thus, similar to the downlink, the uplink resource assignment is carried out in terms of pairs of resource blocks, where each pair consists of two resource blocks in consecutive slots. Uplink Resource Allocation In the upper picture in Figure As an alternative, frequency hopping may be applied for the LTE uplink.
Uplink Frequency Hopping.
Uplink Frequency Hopping 1. Uplink Resource Allocation, the uplink reference signals used for channel estimation are transmitted within the fourth block of each uplink slot12 and with an instantaneous bandwidth equal to the bandwidth of the data transmission.
Note that in the general case uplink frequency hopping may be applied, implying that the two slots of Figure Uplink Resource Allocation are transmitted on different and perhaps substantially separated frequencies. In this case, interpolation between the two reference-signal blocks of a subframe may not be possible as the channel may differ substantially between the two blocks due to the frequency separation.
This is because there are too few Zadoff-Chu sequences available at such short sequence lengths. The intention with the sounding reference signals is for the network to be able to estimate the channel quality of the uplink channel for different UEs in order to be able to apply uplink channel- dependent scheduling.
The sounding reference signals can also be used to estimate the timing of UE transmissions and to derive timing-control commands for uplink time alignment. Sounding reference signals are transmitted independently of the transmission of any uplink data, i.
Furthermore, the sounding-reference-signal bandwidth can very well be, and typically is, different from that of any simultaneous data transmission from the same UE, see Figure The basic principles for generating the channel-sounding reference signals are similar to those of the demodulation reference signals, with basically one difference: The frequency-domain reference-signal sequence the same sequences as for the uplink demodulation reference signal sequences is mapped to every second input of the IFFT.
User 1 User 2 On On e e sub slot -fra 0. Assuming no uplink spatial multiplexing, only a single transport block, of dynamic size, is transmitted for each TTI. Note that the uplink transport format is completely decided by the scheduler in the eNB. Consequently, and in contrast to HSPA, there is no need for signaling the transport format in the uplink control signaling. Two different cases can be differentiated with respect to transmission of uplink control signaling: In this case the uplink control signaling is transmitted on the PUSCH in order to preserve the single-carrier properties.
Obviously, as the terminal has been assigned UL-SCH resources, there is no need to support transmission of the scheduling request in this case. In order to provide frequency diversity these frequency resources are frequency hopping on the slot boundary, i. Therefore, to efficiently exploit the resources set aside for control signaling, multiple terminals can share the same resource block.
The resource used by a PUCCH is therefore not only specified in the time- frequency domain by the resource-block pair, but also by the cyclic shift and, for format 1A and 1B, additionally by an orthogonal cover as described further below. Typically, up to six cyclic shifts can be used in a cell. The length CAZAC sequence is generated as different phase rotations of the uplink reference signals.
Format 1A supports a single acknowledgement bit to be used in case of one code word. Format 1B supports two acknowledgement bits for the case of using two code words. Then scrambling is applied to all the symbols. Different scrambling codes will be used in the two different slots within one subframe. Orthogonal cover sequences are applied to both the four information symbols in a slot as well as to the three reference signal symbols. Thus, with three 14 reference symbols per slot, up to three orthogonal cover sequences can be used which implies three different UEs acknowledgements can be transmitted at the same cyclic shift.
The overall structure is similar to that used for hybrid-ARQ acknowledgements. Each active terminal is assigned a dedicated resource for scheduling request through RRC signaling, providing the possibility to request an uplink grant every x subframe.
If the UE do not want more scheduling, then it will not transmit anything on the dedicated resources. The CQI reports are coded and scrambled. The scrambled bits are then modulated using QPSK, resulting in ten complex-valued symbols. The same structure is used for extended cyclic prefix but with only two reference signals per slot. In that case format 2A or 2B is used. However, it is also possible to mix different formats, i.
This is then signaled by higher layers. The mapping of the control signaling is defined such that the control signaling is located next to the reference signals as illustrated in Figure The reason for this is to improve the decoding performance of the critical control signaling as the channel estimates are of better quality close to the reference symbols.
For data, this is not as critical as, unlike control signaling, hybrid-ARQ retransmissions can be used. Instead, the acknowledgements are punctured in to the coded bit stream. The structure of the feedback depends on whether or not spatial multiplexing is used. Without spatial multiplexing only one layer, with or without TX diversity , only the Channel Quality Indicator CQI , the recommended transport format based on measurements on the reference signals, is sent from the user equipment to the RBS.
Without spatial multiplexing, reporting mode is used. The CQI reflects the recommended transport format of the modulation scheme and coding rate. The structure depends on whether open or closed loop spatial multiplexing is used. The number of CQI resources per slot is configurable. The periodicity of the reporting is common for all user equipment in the cell.
This leads to higher cell capacity and the control of the maximum data rate for User Equipments UE at cell edge. In addition, it helps to prolong the battery life of the UE. In both cases, a parameterized open loop combined with a closed loop mechanism is used.
Roughly, the open loop part is used to set a point of operation, around which the closed loop component operates. Different parameters targets and 'partial compensation factors' for user and control plane are used. This may be used by the eNB as an input to power control and scheduling. Other parameters may also be taken into account, such as UE power headroom, scheduled bandwidth, buffer content and acceptable delay. Rapid interference variations make it difficult to predict the link quality accurately, and select MCS based on such knowledge.
Instead, preliminary, MCS selection is based on averaged link quality.
This however leads to limited throughput as often an unnecessary robust MCS is used. This will instead lead to a larger number of retransmissions and hence a larger delay.
The random access RA serves as an uplink control procedure to enable the UE to access the network. Although the UE can time synchronize to the downlink broadcast control channels BCCH , due to the propagation round-trip delay, there will be a timing uncertainty in the uplink. Therefore, the RA shall reserve a sufficient time window to accommodate various arrival times. Collisions may occur and an appropriate contention-resolution scheme needs to be implemented. Including user data on the contention-based uplink is not spectrally efficient due to the need for guard periods and retransmissions.
Therefore, it has been decided to separate the transmission of the random access preamble, the purpose of which is to obtain uplink synchronization, from the transmission of user data.
Random Access 4. The resources used for the non-synchronized RA and the format of the preamble are further clarified in the following two sections. In the first steps 1, 2, 3, 4, 5 , the UE obtains uplink synchronization and is assigned resources for uplink transmission.
During the next steps 6, 7, 8 , uplink transmission is synchronized. The UE transmits information on the scheduled resource, e. The UE is then able to transmit the RA message 3. If no response has been received UE increases the power and tries again until it gets a response or until it reaches the maximum allowed retransmissions. In this case a failure will be indicated to the upper layers. The timing misalignment amounts to 6.
Here the preamble length is then A guard time of Longer guard periods and cyclic prefix are needed to accommodate timing uncertainties from cells larger than 15 km.
Such large cells may also require longer preambles to increase the received energy. These larger slots are created by the eNB by not scheduling traffic in the consecutive subframe s. This preamble format can only be transmitted in UpPTS. The effective bandwidth utilized by the RA preamble is 1.
This is necessary since RA and regular uplink data are separated in frequency-domain but are not completely orthogonal. For FDD systems, RA opportunities do not occur simultaneously in different frequency bands but are separated in time. This spreads out processing load in the RA receiver. In total 16 such configurations are defined, ranging from one RA opportunity every 20 ms very low RA load to one every 1 ms very high RA load.
The rather small bandwidth of 1. Furthermore all RA preambles fit into all defined spectrum allocations enabling the same preamble formats for all spectrum allocations. It is up to the base station implementation how to handle this overlap. Here only one 1.
The preamble implicitly includes a random ID which identifies the UE. LTE provides for each cell 64 such random IDs and thus 64 preambles. The upper picture in Figure shows the detailed timing of the basic random- access preamble.
The preamble starts with a cyclic prefix CP to enable simple frequency-domain processing. Format 1 has an extended CP and is suited for a cell radius up to approximately 80 km. However, since no repetition occurs this format is only suited for environments with good propagation conditions. This format supports cell radii of up to approximately 30 km. Format 3 also contains a repeated sequence and an extended CP. Using a RA opportunity length of 3 ms this format supports cell radius of up to approximately km.
In opposite to format 1 format 3 contains a repeated sequence and is therefore better suited for environments with bad propagation conditions.
Format 4 has a guard period of 0. However, there are some exception cases. The Zadoff-Chu sequence length is in case of preamble format 4.
Out of one Zadoff-Chu sequence — in the following also denoted root sequence — multiple preamble sequences can be derived by cyclic shifting: Due to the ideal ACF of Zadoff-Chu sequence multiple mutually orthogonal sequences can be derived from a single root sequence by cyclic shifting one root sequence multiple times the maximum allowed round trip time plus delay spread in time-domain.
The correlation of such a cyclic shifted sequence and the underlying root sequence has its peak no longer at zero but at the cyclic shift. If the received signal has now a valid round trip delay — i. For small cells up to 1. In larger cells not all sequences can be derived from a single root sequence and multiple root sequences must be allocated to a cell.
Sequences derived from different root sequences are not orthogonal to each other. Additional preamble sequences, in case 64 preambles cannot be generated from a single root Zadoff-Chu sequence, are obtained from the root sequences with the consecutive logical indexes until all the 64 sequences are found. More details on the creation of the preambles can be found in TS A frequency-offset creates an additional correlation peak in time-domain.
A frequency offset has to be considered high if it becomes substantial relative to the RA subcarrier spacing of Hz, e. The offset of the second correlation peak relative to the main peak depends on the root sequence. An offset smaller than TCS may lead to wrong timing estimates whereas values larger than TCS increase the false alarm rate.
In order to cope with this problem LTE has a high-speed mode 19 or better high frequency offset mode which disables certain cyclic shift values and root sequences so that transmitted preamble and round trip time can uniquely be identified. Additionally a special receiver combining both correlation peaks is required. NCS value Range [km] NCS configuration Normal High-speed 0 0 15 1 1 13 18 2 2 15 22 3 18 26 3 4 22 32 5 26 38 4 6 32 46 5 7 38 55 6 8 46 68 9 59 82 10 76 11 93 12 13 14 59 15 - Figure Note that only for high speed there is a RSindex range limitation, see Figure 3- Root Sequence need - Unrestricted Set cellRange Number of RACH Root Allowed [km] Sequences NRS rachRootSequence interval 4 11 52 - 5 13 64 - 6 16 76 - 7 19 90 - 26 - 30 - 39 - 54 - 64 - 64 - 64 - Figure This sets the parameter rachRootSequence for each cell based on its PCI allocation, highspeed-flag and cell range.
This can reduce false preamble detection, which will improve UE accessibility. For more information on the feature refer to L13 to L14 Delta course. Only a terminal which finds a match between the identity received and the identity transmitted declares if the random access procedure successful. If the random access procedure is deemed to be successful the UE transmits an acknowledgment in the uplink. Terminals which do not find a match between the identity received and the respective identity transmitted are considered to have failed the random access procedure and must restart the random access procedure.
If UEs set their transmit timing based only on the timing of the received downlink timing, their corresponding uplink transmissions will thus arrive at the cell site with potentially very different timing. If these receive-timing differences are too large, the orthogonality between the uplink transmissions of different UEs will not be retained.
Thus, an active uplink transmit-timing control is needed to ensure that uplink transmissions from different UEs are received with approximately the same timing at the cell site. The transmit-timing control operates such that the network measures the received uplink timing of the different UEs. Similarly, a UE can be ordered to retard its transmit timing. The timing advance command indicates the change of the uplink timing relative to the current uplink timing as multiples of 16 Ts.
NTA is the timing offset between uplink and downlink radio frames at the UE, expressed in units of Ts. Ts is defined by: This corresponds to a distance of m. Here, adjustment of NTA value by a positive or a negative amount indicates advancing or delaying the uplink transmission timing by a given amount respectively. Uplink Transmit-Timing Control Continued If the received downlink timing changes and is not compensated or is only partly compensated by the uplink timing adjustment without timing advance command, the UE changes NTA accordingly.
As long as a UE carries out uplink data transmission, this can be used by the receiving cell site to estimate the uplink receive timing and can thus as a source for the timing-control commands. When there is no data available for uplink, the UE may still carry out transmission of sounding reference signals with a certain period, to continue to enable uplink receive-timing estimation and thus retain uplink time alignment.
In this way, the UE can immediately restart uplink- orthogonal data transmission without the need for a timing re-alignment phase. In that case, uplink time alignment may be lost and restart of data transmission must then be preceded by an explicit timing- re-alignment phase random access to restore the uplink time alignment.
Low SINR limits the uplink throughput. The radio units of the reception points must be served by the same digital unit. UL CoMP combines signals between single-sector cells such as those not between combined cells.
Cell border means sector border. The cell-border user uplink throughput gains depend on the load and the scenario.
The gain is significant in a scenario where the UE is connected to a macro cell being close to a micro cell but will also be beneficial for a user that is located between two macro cells. If the uplink load is high, also users that are not on cell border may benefit from the feature since the cell-edge users finish their transmissions quicker. Main benefit for UEs at cell borders Figure The feature adaptively selects two sector carriers, primary and secondary, to receive signals from a UE.
When a UE is at the border between two cells, the combinations of the two selected sector carriers can increase the UE uplink throughput.
This feature is not supported in the micro RBS. The two sector carriers to combine are selected as shown in Figure Sector Selection A UE has a primary sector. The primary sector is always in the serving cell of the UE. This feature supports the following sector carrier combination scenarios: LTE performance in uplink depends on uplink synchronization.
The following new MOM attributes are presented in Figure Uplink Synchronization They may be set in the small cell to enable simultaneous synchronization to small cell and macro cell. The maximum distance between reception points is 1. There is no need to adjust synchronization between macro cells. The maximum number of uplink physical resource blocks that may be scheduled in a Time Transmission Interval TTI is determined by two times the number of antennas in the cell with the maximum number of antennas.
Interference Rejection Combining is required. Scheduling is used both in uplink and downlink. In the downlink the RBS schedules different physical channels and also allocates scheduling blocks with data intended for different UEs.
The scheduler is in other words located in the RBS and is responsible for both uplink and downlink. It is also used when Inter Radio Access Technology handovers are required, e. In case of MIMO the resource allocation is the same for all streams. Channel variations can be exploited for multi-user diversity i. In the downlink, the scheduler may assign a set of resource blocks to a user according to the agreed PDCCH scheme, while in the uplink resource blocks assigned to a specific user must be contiguous in the frequency to preserve the SC-FDMA structure.
Also only a limited set of DFT sizes will be allowed, i. This further limits the number of RB that can be assigned to a user. When this is not possible due to resource limitations the scheduler performs prioritization between users and logical channels according to the QoS requirements. In the downlink, where the eNB has immediate access to the transmit buffers of the radio bearers, the scheduler performs the prioritization both between users and different radio bearers of a user.
In the UL on the other hand the scheduler only prioritizes between different users based on buffer status reports. The prioritization between different logical channels within one UE will be done in the UE with assistance from the network. When user equipment has several radio bearers, the user equipment performs the prioritization between the radio bearers and is referred to as the user equipment rate control function.
Although fast dynamic scheduling is the base line for LTE scheduling, several methods for limiting the control signaling demands for services such as speech VoIP where small packets are generated regularly have been discussed in 3GPP. Link Adaptation, which includes transport format selection, is closely related to scheduling and the two functions interact by exchanging information prior to each scheduling decision. The operator controls part of the scheduling behavior via the QoS framework.
The resources handled by the Scheduler are: It enables users to be multiplexed and scheduled simultaneously and facilitates efficient use of spectral and hardware resources for optimization of user throughput and cell capacity. Amongst the currently supported scheduling strategies, the LTE Scheduler supports fair distribution of resources between users and its variants as well as priority for robust system control signaling. More details on the available Scheduling Strategies can be seen on the Figure below: Equal rate is the most fair variant of the proportional fair scheduling Equal Rate algorithms.
It strives to give users an equal rate. Proportional Fair High is a high fairness variant of the proportional fair Proportional Fair High scheduling algorithm. Proportional Fair Medium is a medium fairness variant of the proportional fair Proportional Fair Medium scheduling algorithm.
Available Scheduling Strategies The Scheduler is part of the basic LTE functions and part of radio resource management, designed to provide optimal performance and capacity at all times by automatically adapting to variations in traffic load and distribution. The automated behavior reduces the need for configuration and optimization to adapt to the concepts of the Self Organizing Network and Smart Simplicity.
A higher scheduling priority gives the radio bearer a higher probability of obtaining resources and enables the user equipment to perform transmission or reception. The allocation of resources is made per user equipment. The user equipment priority is defined as the highest scheduling priority of the radio bearers belonging to the user equipment, including retransmissions.
The user equipment with the highest priority is selected first for transmission. In the uplink, when the user equipment has many radio bearers, they are grouped into Logical Channel Groups LCGs, also sometimes referred to as radio bearer groups.
The buffer status report is then expanded so it reports the buffer status per radio bearer group. Each LCG is given a certain priority. The Scheduler controls all radio interface resources, except the following physical signal and channel transmissions, as shown in Figure Common channels 2. Initial transmissions of DCCH 4. Transmissions of random access msg 3 2.
HARQ retransmissions 3. SRB1 has the highest priority.
No scheduling grants need to be transmitted for the synchronous retransmissions in the uplink. At the beginning of each transmission time interval, the Scheduler receives information on available resource blocks, and available downlink power in the cell.
The Scheduler, together with Link Adaptation and power control then assigns an appropriate amount of resources to the UE. Thus, a scheduling block can consist of both user data and control data.
With Round Robin, the scheduling decisions are mainly delay-based not to be confused with Delay Scheduling. With Proportional Fair, the scheduling decisions are channel dependent in time, which to some extent will lead to prioritization of users with good radio conditions. The scheduling strategy is configurable per RBS. The operator can configure the number of PUCCH resources for the scheduling request and the Channel Quality Indicator CQI to control the trade-off between the number of supported users and the uplink peak throughput.
To support fast channel dependent link adaptation and channel dependent time and frequency domain scheduling the UE may be configured to report the Channel Quality Indicator CQI reports. For TDD the channel reciprocity could be utilized for channel dependent scheduling to some extent, although one must keep in mind that even if the fading characteristics are reciprocal in TDD the UL and DL will experience different interference and there might be an unbalance in path gain between uplink and downlink.
Based on the CQI reports and QoS requirements of the different logical channels the scheduler assigns time and frequency resources, i. The UE monitors the control channels to determine if it is scheduled on the shared channel PDSCH and if so, on what physical layer resources to find the scheduled data. In the downlink, the physical resource blocks are assigned from lower frequencies to higher, that is from left to right. The starting point in frequency is configurable per cell.
This enables some basic frequency planning, for example in problem areas. To increase frequency diversity and at the same time keep intercell interference at low levels, the Random Frequency Allocation can be activated to automatically and randomly select the starting point. For example, with a 20 MHz bandwidth there are roughly resource blocks. In 3GPP it is agreed to allow for several types of CQI reports ranging from a single wideband report to a report containing frequency granular information multi-band and MIMO information.
The set of subbands, S, is semi-statically configured through higher layer signaling RRC. A step size of 2 dB is used. In both cases a wideband average is computed and used as a reference. In addition, M subbands M could be fixed or configured are selected and encoded differentially using two bits relative to the wideband average.
The UE internal procedure to select subbands is not specified but the selected subbands should correspond to the highest CQI values. The supported subband sizes and M values are a function of system bandwidths. In addition to channel quality information, the UE also reports information on the preferred transmission rank, in the case of spatial multiplexing. UL Scheduling Mechanism and Figure Uplink Scheduling.
This means that the UE is mandated to use a certain transport format and that the eNB is already aware of the transmission parameters when detecting the UL data transmission. This reduces the amount of control signaling required in the uplink, which is important from a coverage perspective, especially with the short 1 ms TTI.
The eNB may configure the UE to transmit a wideband sounding reference signal that can be used for estimating the UL channel quality. Scheduling resources among users in the uplink is complicated by the fact that the scheduler is situated in the eNB and is not automatically aware of the users resource demand, i. The concept for uplink scheduling suggested is based on a resource reservation principle. In addition, the resources are autonomously revoked when the UE loses UL synchronization.
The purpose is to enable UE to rapidly request resources for uplink data transmission. For the dedicated approach, each active user is assigned a dedicated channel for performing the scheduling request. The benefit with this method is that no UE ID has to be transmitted explicitly since the UE is identified by the channel used.
From a scheduling request the scheduler has limited knowledge of what type of data and of what priority the UE has. For further information a grant is issued by the scheduler. The grant addresses a UE and not a specific logical channel.
A BSR is triggered when at least one of the following criteria is fulfilled: The scheduling request uses PUCCH format 1 and the number of scheduling request users per cell is configurable with a parameter that sets the number of users that are allocated scheduling request resources.
The configurable periodicity of the scheduling request is 5,10, 20… ms, and equal for all user equipment in the cell. If no scheduling request resources are allocated on PUCCH for the user equipment, the user equipment uses the random access process to request resources.
When user equipment is scheduled in a subframe, the uplink scheduler transmits a scheduling grant to the user equipment on PDSCH, indicating the resource blocks and transport format to use for uplink transmission. In cooperation with the link adaptation and power control functionality the uplink scheduler use an estimated buffer, based on BSR, together with the channel quality information to assign an appropriate number of resource blocks to user equipment in the uplink.
This is achieved by sending UL scheduling grants without explicit scheduling request from the UE side. The user plane latency is reduced due to less signaling. Prescheduling grants are only sent in low load situation. Different versions of speed-test are commonly used by smart phones users to measure bandwidth quality. Pre-scheduling is automatically deactivated timer controlled to reduce the impact on UE power consumption The comparison of Prescheduling off and on is illustrated in Figure and Figure below.
Numbers are example only Figure Prescheduling ON The Operator benefits are: The device has to respond even if there is no data to send.
Transport format selection includes selecting the modulation and coding scheme and transport block size. In the downlink, the selection is channel dependent because Link Adaptation uses CQI reports from the user equipment to adapt the transmissions to current radio conditions. Link Adaptation 3. Antenna mapping, part of Link Adaptation, controls multi-antenna transmission by deciding the antenna mapping mode TX diversity, spatial multiplexing or beamforming, as well as submodes within each mode , spatial multiplexing rank and spatial multiplexing precoding matrix.
Channel prediction, also part of Link Adaptation, provides information needed for decisions in the other Link Adaptation functions and Power Control. It includes collecting channel measurements, made in the downlink by the user equipment and sent to the RBS in channel feedback reports containing CQI, precoding matrix indicator PMI , and rank indicator RI.
The SINR is based on measurements on the uplink demodulation reference signal. The transport format selection influences the scheduling decision, so the scheduling decision is implicitly influenced by channel quality estimations CQI for downlink and SINR for uplink. Link Adaptation is not used in the uplink for random access message 3 RRC connection request or retransmissions.
In the latter case, the same transport format is used, as was used in the initial transmission The Scheduler retrieves information about the number of scheduling blocks and MCS to use in uplink 4 Inter-Cell Interference Coordination ICIC Inter-cell Interference Coordination, located in eNB, has the task of managing radio resources notably the radio resource blocks such that inter-cell interference is kept under control.
ICIC is inherently a multi-cell RRM function that needs to take into account the resource usage status and traffic load situation of multiple cells. Uplink inter-cell interference coordination consists of two inter-related mechanisms, the details of which are currently being discussed within the 3GPP. The first part is a pro-active ICIC mechanism. The basic idea of this scheme is that a potentially disturbing eNB pro-actively sends a resource block specific indication to its potentially disturbed neighbor.
This message indicates which resource blocks will be scheduled with a high probability with high power i. Thus this message allows the receiving eNB s to try to avoid scheduling the same resource blocks for its cell edge UEs. In addition, the 3GPP also discusses the use of the overload indicator OI that was originally proposed for inter-cell power control purposes.
It is currently agreed in 3GPP that the OI also carries information at the resource block granularity.
As opposed to the pro-active scheme, the overload indication is a reactive scheme that indicates a high detected interference level on a specific resource block to neighbor eNB s. Interference rejection combining IRC is another method to suppress inter-cell interference. IRC utilizes correlation in the spatial domain between antennas and in the frequency domain to suppress interfering signals from other cells.
The suppression can be seen as weighting down the signal in the direction of an interferer, so that it does not corrupt the signal from the desired user. This will improve capacity and performance in interference impacted situations. IRC is most effective with a limited number of interferers and with high SNR on both signal and interferer. The purpose of LB is thus to influence the load distribution in such a manner that radio resources remain highly utilized and the QoS of in-progress sessions is maintained to the largest possible extent while call dropping probabilities are kept sufficiently small.
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Security of Mobile Communications The explosive call for for cellular communications is using the advance of instant expertise at an unparalleled speed. Metro Ethernet Services for LTE Backhaul Artech House Mobile Communications Library The backhaul component of the community is created from intermediate hyperlinks among the center community and the small sub-networks on the "edge" of the complete hierarchical community.
Rated 4. Download Accidental Immigrants and the Search for Home: Women, by Carol E. Close Preview. Toggle navigation Additional Book Information. Description Table of Contents Author s Bio. Summary Opportunities are at hand for professionals eager to learn and apply the latest theories and practices in air interface technologies.
After a general description of wireless cellular technology evolution and the performance targets and major technical features of LTE-Advanced, LTE-Advanced Air Interface Technology discusses various innovative technical features in detail, including Innovative concepts in carrier aggregation techniques Collaborative multipoint CoMP theory and performance analysis Enhanced multiantenna solutions or multiple-input, multiple-output MIMO technology, in particular, multiuser and multilayer MIMO Relaying issues Self-organizing and heterogeneous networks Interference suppression and enhanced intercell interference coordination eICIC technology This book opens the door of LTE-A technology for practitioners in any stage of wireless communications.
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