Path Balance on Distributed Antenna Systems Presentation by Dennis McColl - April 2nd, 2013 PUSCH PUCCH.

Path Balance on Distributed Antenna Systems Presentation by Dennis McColl - April 2nd, 2013
PUSCH PUCCH

Agenda What does path an unbalanced cell/sector look like?
Why do we care about Rise Over Thermal (ROT)? Why doesn’t the UE just increase power? How does uplink power control work in CDMA and EVDO? How does LTE manage uplink power control? Where does the path imbalance come from? What causes reverse link rise in an unbalanced system? Is there an easy way to estimate path balance in CDMA, EVDO, and LTE? What if I want more accurate path balance measurements? What if this is a “Neutral Host DAS” and I don’t have control or access? Summary of measurement methods with examples. What are the potential impacts of a path imbalance?

Inter-Cell Interference
Unbalanced reverse link paths are susceptible to receiving or generating inter-cell interference. When the UE moves one seat over and hands to the adjacent balanced cell at a similar RSRP it will transmit at normal power while still in range of the DAS system. The eNodeB receive noise floor is raised when the UE hands out but is still within range. UE is uploading on a DAS sector with a reverse link favored imbalance. The UE has only moved a couple of feet but has handed to a normal macro cell. Inter-Cell Interference Two FTP Upload Examples: A UE performs an upload on the imbalanced sector then moves to an adjacent sector and performs a second upload. View is from eNodeB RxOut Port of the unbalanced cell Reverse Link is about 15dB Better than the Forward Link

Free Space Path Loss -Balanced Path-
A lot of work has been done to minimize the effects of inter-cell interference in wireless. Path balance is a basic assumption. Cocktail parties and full-duplex wireless communications generally work much better if everyone involved uses just enough volume to hold a conversation. Free Space = Balanced * *As long as the change in frequency is not significant.

If the radio path is unbalanced, increases in reverse link noise will dramatically affect uplink throughput long before the downlink throughput changes. Modulation Code Scheme selection will favor increased error correction and lower modulation schemes as noise increases. More Rx Noise UL = Upload DL= Download

Addt’l UE Tx Pwr during download is due to more
The UE transmit power remains unchanged as noise power increases maintaining a stable receive noise level at every eNodeB. UE Tx During Upload remains Stable but modulation Coding schemes change to accommodate reduced SINR Average UE transmit power adds PUCCH and PUSCH power which is less predictable than treating them separately. Future testing should report PUCCH/PUSCH separately. QPSK Acks. + Error Corr. Ex. 64 QAM The PUCCH is more robust than the PUSCH resulting in delayed downlink impact. (Uplink throughput will suffer with poor path balance and noise) Addt’l UE Tx Pwr during download is due to more error correction messaging needed as Rvs noise increases. QPSK Acks. UL = Upload DL= Download Ex. QPSK More Rx Noise

The eNodeB Receive Noise Floor needs to be low and stay low.
Uplink throughput is determined by UE distance from the cell, loading, and rise over thermal. We can’t have random UE’s powering up Willy-nilly. (Best Channel Power Density for an Ericsson eNodeB measured at the RxOut port is about -156dBm/Hz.)

Using the ‘minimum hold’ trace option will allow for noise floor measurements at any time of day. The longer it cooks, the lower it will go so be sure to be consistent when comparing measurements. (Best Channel Power Density for an Ericsson eNodeB measured at the RxOut port is about -156dBm/Hz.)

What does ‘Normal’ look like?
Characterizing normal LTE balanced path operation Closed Loop Testing at EnodeB (Ideal Environment) The difference in transmitted power between the two physical channels is due to their bandwidth and P0NominalTarget levels. UE Average PUSCH Power During Upload UL = Upload DL= Download UE Average PUCCH Power During Download Moving to Cell Edge

Shows expected performance with increased pathloss.
Throughput suffers at strong RSRP’s but essentially stays flat when the UE is in its linear dynamic range. Download Throughput Degradation at RSRP < -100dBm Likely Caused By PCI Ingress into Experimental Setup UL = Upload DL= Download UL = Upload DL= Download

?!?!? It appears that UE performance degrades when the power control process goes non-linear. When RSRP exceeds -46dBm (in a balanced system) the UE’s performance degrades significantly and the eNodeB PUSCH and PUCCH noise floors start rising?!?!?!? Throughput suffers at strong RSRP’s but essentially stays flat when the UE is in its linear dynamic range. Download Throughput Degradation at RSRP < -100dBm Likely Caused By PCI Ingress into Experimental Setup ?!?!? UL = Upload DL= Download UL = Upload DL= Download

PUSCH is still stable at this point. Normal PUCCH Target Level
PUCCH During Download on al FL/RL balanced system. Trace A at an RSRP of -36dBm (Rev Link PL =21dBm–(-36dBm)=57dB Trace C at an RSRP of -46dBm (Rev Link PL =21dBm–(-46dBm)=67dB Note the 10dB increase between a normal PUCCH (Trace C) and 10dB after it reached it’s lowest transmit power.(Trace A). PUSCH is still stable at this point. Normal PUCCH Target Level

Normal PUCCH Target Level
PUCCH During Download on al FL/RL balanced system. Trace A at an RSRP of -28dBm (Rev Link PL =21dBm–(-36dBm)=57dB Trace C at an RSRP of -46dBm (Rev Link PL =21dBm–(-46dBm)=67dB Note the 18dB increase between a normal PUCCH target and 10dB after the UE reached it’s lowest PUCCH power. The UE PUSCH power reached its minimum transmit ability 2dB ago and is now raising receive levels. Normal PUCCH Target Level

Power Control on CDMA and EVDO Systems
Open Loop Estimate: Based on received signal strength, a frequency specific adjustment, and offsets. Access Probe adjustments ‘learned’ during setup are included in initial traffic power settings before the closed loop starts. Closed Loop Adjustments: Based on Eb/No. When in soft-handoff the mobile will power down until all sectors involved in soft- handoff command the mobile power to be raised. Transmit Gain Adjust Transmit Gain Adjust is the difference between open loop estimate and the closed loop steady state. Calculated at the mobile. Open Loop Estimate: Mobile Transmit (dBm) = - Mobile Receive (dBm) + Path Loss Estimate + Offsets 800MHz Path Loss Estimate is 73dB 1900MHz Path Loss Estimate is 76dB **Access Probe adjustments ‘learned’ during setup are included in initial traffic power settings before the closed loop starts. Closed Loop Adjustments: Transmit Gain Adjust The mobile is instructed 800 times a second to raise or lower their transmit power to maintain Eb/No while transmitting on a traffic channel. Transmit Gain Adjust is the difference between open loop estimate and the closed loop steady state. When in soft-handoff the mobile will power down until all sectors involved in soft-handoff command the mobile power to be raised.

Power Control on LTE Systems -
Calculated Forward Link Path Loss: Based on known RS and received RSRP. The Reference Signal transmission power is broadcast by the eNodeB to the UE. The UE derives the path-loss by comparing the measured RSRP to the known Reference Signal transmission Power. This is the Open Loop Closed Loop Adjustments: UE specific power headroom reports, Demodulation Reference Signals (DMRS), and Sounding Reference Signals (SRS) are used to estimate uplink channel condition and quality for uplink transmission control on the PUCCH and PUSCH. LTE Uplink is orthogonal SC-FDMA. Users in the same cell are theoretically orthogonal to each other but adjacent cells and eNodeBs are not. Transmit Gain Adjust is not available for LTE but can be derived based on expected UE PUCCH/PUSCH transmit levels during downloads/uploads given a known RSRP. P0Nominal PUCCH and PUSCH Targets will dictate UE closed loop power targets.

What happens to the normal case if the path is imbalanced???
For a DataPro reading of -60dBm RSRP during an Upload task, the corresponding PUSCH power should show a -14dBm on DataPro UL = Upload DL= Download For DataPro a reading of -60dBm RSRP during a download task, the corresponding PUCCH power should show a -35dBm on DataPro Moving to Cell Edge

A 1dB change in reverse link pathloss will cause the UE transmit power to change 1dB.
UE transmit power requirements change with the reverse link path resulting in a stable reverse link rise at the eNodeB receiver. dBm/Hz

There is no benefit in having a path imbalance.
Download performance doesn’t change. UL = Upload DL= Download Uplink performance only get’s worse.

Lessons Learned So Far Unbalanced paths will never improve performance. An unbalanced path will allow individual UE’s to generate inter-cell interference at cell edges leading to unstable receive noise floors. Rises in reverse link noise floors at eNodeB receivers will slow uplink throughput considerably, well before the downlink is affected. There is a separate reverse link path estimation and power control process in LTE that is similar to CDMA/EVDO but different. LTE UE’s can only reduce their transmit power to a certain point. Reverse link paths with less than 67dB of loss (-46dBm RSRP in a balanced system) at transition boundaries can generate inter-cell interference on the PUCCH. Reverse link paths with less than 52dB of loss (-30dBm RSRP in a balanced system) at transition boundaries can generate inter-cell interference on the PUSCH. Intra-cell UE uplink orthogonality will protect intra-cell users somewhat but the levels above may degrade performance unnecessarily. These conclusions and tests results were based on the LG VL600 UE.

If nothing is done the reverse link
Typical DASystems condition (“attenuate”) forward link signals before optical conversion. Reverse link signals do not need to be conditioned before conversion. Typical delta is 25 to 30dB. Conditioning Final output per antenna location is less than 21dBm per Band after splitting/combining. This represents a forward link loss of 25 to 31dB. 52dBm Independent Forward Link Calibration and Gain Adjustments. Forward Link 850MHz BTS Duplexed Variable Attenuation Reverse Link Antenna Location A 850 MHz 50dBm Forward Link RF to Optical Optical to RF Antenna Location B 1900MHz BTS 1900 MHz Duplexed Variable Attenuation Antenna Location C Reverse Link Optical to RF RF to Optical 750 MHz Antenna Location D 46dBm Forward Link Splitting/ Combining 750 MHz eNodeB Duplexed Independent Reverse Link Gain Adjustments. Variable Attenuation If nothing is done the reverse link will be dB hot. Reverse Link

LTE Uplink Power Control Example
Balanced Forward and Reverse Link Path Forward Link PL = 99dB, Reverse Link PL = 99dB BALANCED User on Balanced System LTE Case: RSRP = -78dBm Calculated Forward Link Pathloss =21dBm – (-78dBm) = 99dB Reverse Link Pathloss = 99dB* (not including LNA) RACH Target = -104dBm (default) PRACH Open Loop Estimate =-104dBm +99=-5dBm P0-NominalPUSCH/PUCCH Target=-106/-113dBm Measured Closed Loop Avg. Tx PUCCH During Download (Balanced System) = -16dBm Measured Closed Loop Avg. Tx PUSCH During Upload (Balanced System) = 4dBm Rx Noise transmitted to adjacent cells on PUCCH and PUSCH ≈ -16dBm and 4dBm

LTE Uplink Power Control Example Unbalanced Forward and Reverse Link
Forward Link PL = 99dB, Reverse Link PL = 79dB UNBALANCED User on Balanced System LTE Case: RSRP = -78dBm Calculated Forward Link Pathloss =21dBm – (-78dBm) = 99dB Reverse Link Pathloss = 79dB* (not including LNA) RACH Target = -104dBm (default) PRACH Open Loop Estimate =-104dBm +99=-5dBm P0-NominalPUSCH/PUCCH Target=-106/-113dBm Measured Closed Loop Avg. Tx PUCCH During Download (Unbalanced System) = -37dBm Measured Closed Loop Avg. Tx PUSCH During Upload (Unbalanced System) = -16dBm Rx Noise transmitted to adjacent cells on PUCCH and PUSCH ≈ -37dBm and -16dBm

Equal Power Handoff Region with Imbalance
In this case, the unbalanced DAS system must manage increased inter-cell interference when a UE hands out or is on an adjacent cell when near the cell edge. UNBALANCED BALANCED User on DAS System LTE Case: RSRP = -78dBm Calculated FL PL=21dBm – (-78dBm) = 99dB Reverse Link Pathloss = 79dB* (Not Including LNA) PRACH Target = -104dBm (default) PRACH Open Loop Estimate =-104dBm +99=-5dBm P0-NominalPUSCH/PUCCH Target=-106/-113dBm Measured Closed Loop Avg. Tx PUCCH During Download (Unbalanced System) = -37dBm Measured Closed Loop Avg. Tx PUSCH During Upload (Unbalanced System) = -16dBm Rx Noise from Adjacent UE PUCCH/PUSCH ≈ -16dBm/4dBm User on Macrocell (or Adjacent DAS) LTE Case: RSRP = -78dBm Calculated FL PL=21dBm – (-78dBm) = 99dB Reverse Link Pathloss = 99dB* RACH Target = -104dBm (default) PRACH Open Loop Estimate =-104dBm +99=-5dBm P0-NominalPUSCH/PUCCH Target=-106/-113dBm Measured Closed Loop Avg. Tx PUCCH During Download (Balanced System) = -16dBm Measured Closed Loop Avg. Tx PUSCH During Upload (Balanced System) = 4dBm Rx Noise from Adjacent UE PUCCH/PUSCH ≈ -37dBm/-16dBm (C/I≈-20dB) (C/I≈-20dB)

Most large venues will inevitably have multiple areas that are served by both DAS and macro systems that are susceptible to inter-cell interference. “Ballpark” macro cell.

Yes!! Use the mobile reported Transmit Gain Adjust on DPDM.
800MHz CDMA Using DPDM 1900MHz EVDO Using DPDM TGA values should match the macro system. Typical values -5dB to -15dB.

What about LTE? There’s no transmit gain adjust in LTE but UE transmit power changes linearly with path loss so an “LTE Transmit Gain Adjust” can be inferrred. On an unloaded system at a constant RSRP, UE transmit power is predictable under specific conditions. Average PUCCH Transmit Power should reach an approximately steady state while downloading. Average PUSCH Transmit Power should reach an approximately steady state while uploading. Deviations from the expected values are path imbalances when compared to normal balanced path operation.

Characterizing normal LTE balanced path operation
Closed Loop Testing at EnodeB (Ideal Environment) For a DataPro reading of -48dBm RSRP during an Upload task, the corresponding PUSCH power should show a -27dBm on DataPro UL = Upload DL= Download For DataPro a reading of -48dBm RSRP during a download task, the corresponding PUCCH power should show a -44dBm on DataPro Moving to Cell Edge

Do these transmit levels indicate a balanced system?
Power Control on LTE Systems Deriving an LTE Version of TGA Using PUCCH/PUSCH Average Transmit Power -DPDM During Upload – Given any RSRP, Path Balance can be estimated using the Average PUSCH Transmit Power. Do these transmit levels indicate a balanced system? -DPDM During Download – Given any RSRP, Path Balance can be estimated using the Average PUSCH Transmit Power.

-DPDM During Download –
The UE has to transmit 10dB hotter than expected, increasing inter-cell interference on adjacent cells and the macro system. -DPDM During Upload – Given any RSRP, Path Balance can be estimated using the Average PUSCH Transmit Power. No, in this case the reverse link pathloss is about 10dB greater than the forward link. -DPDM During Download – Given any RSRP, Path Balance can be estimated using the Average PUSCH Transmit Power.

Couplers can be used if available at both the head end and remote locations. Signals can be measured or injected. Known Pilot and Reference Signal levels can be measured at remote couplers. The difference (minus coupling) is the forward path loss. Pilot, Reference Signal, and composite power levels can also be measured at the BTS. The difference (minus coupling) from this level to the remote measurement is the forward path loss. Reverse link measurements can be made at a receive port if available. Gain may be present as a part of the reverse link itself and should be compensated for (removed) in the path calculation. If a continuous wave or simulated LTE signal (VSG) is applied at a coupled port at the remote, the coupling values will have to be accounted for in the path calculation.

Remotes may also have couplers available.
Accurate forward link measurements can be made at a coupled port if installed at the remote. Coupling values will be different per band. Pilot, RSRP, Channel Power can be measured. Signals may also be injected using the coupled port for reverse path measurements assuming the coupled port is bi-directional. Coupling values will be different per band. Potential injected signals for reverse link measurements: Continuous Wave (CW) Vector Signal Generator (VSG)

A VSG with a -25dBm RSRP at any frequency allows
for channel and quality estimation on any frequency.

Forward Path Measurement with Couplers Using measured Pilots, Reference Signals, or composite powers. Coupling factor changes with frequency and model. Coupling factor changes with frequency and model. DAS Transmitter Directional Coupler Directional Coupler Receiver With +20dB gain. A B RxOut (≈+20dB from Duplexed Port) ( ) ( ) A + Coupling Factor-A - B + Coupling Factor-B Forward Link Pathloss = *Coupling factors are positive in this case.

Forward Path Measurement with Couplers Using known Pilots or Reference Signals
Coupling factor changes with frequency and model. Coupling factor changes with frequency and model. DAS Transmitter Directional Coupler Directional Coupler Receiver With +20dB gain. B RxOut (≈+20dB from Duplexed Port) ( ) A - B + Coupling Factor-B Forward Link Pathloss = CDMA Pilot = 33dBm EVDO Pilot = 41dBm Ref. Signal = 21dBm A *Coupling factor is positive in this case.

Reverse Path Measurement with Remote Coupler Using an injected Vector Signal Generator or CW
Coupling factor changes with frequency and model. Coupling factor changes with frequency and model. DAS Transmitter Directional Coupler Directional Coupler Receiver With +20dB gain. A RxOut (≈+20dB from Duplexed Port) B ( ) ( ) A - Coupling Factor-A - B - LNA Gain Reverse Link Pathloss = *Coupling factor is positive in this case.

Forward Path Measurement Over the Air Using measured Pilots, Reference Signals, or composite powers.
Coupling factor changes with frequency and model. Coupling factor changes with frequency and model. DAS Transmitter Directional Coupler Directional Coupler Receiver With +20dB gain. A RxOut (≈+20dB from ‘A’) B ( ) A + Coupling Factor-A - B Forward Link Pathloss = *Coupling factor is positive in this case.

Forward Path Measurement Over the Air Using known Pilots or Reference Signals
Coupling factor changes with frequency and model. Coupling factor changes with frequency and model. DAS Transmitter Directional Coupler Directional Coupler Receiver With +20dB gain. RxOut (≈+20dB from ‘A’) B - A B Forward Link Pathloss = CDMA Pilot = 33dBm EVDO Pilot = 41dBm Ref. Signal = 21dBm A

Reverse Path Measurement Over the Air Using a Transmitted Signal
Coupling factor changes with frequency and model. Coupling factor changes with frequency and model. DAS Transmitter Directional Coupler Directional Coupler Receiver With +20dB gain. RxOut (≈+20dB from ‘A’) A B ( ) - A B - LNA Gain Reverse Link Pathloss =

Field measurements are less accurate but may be necessary if a coupler is not available or if you are working on a neutral host system. Field measurements and transmissions will be subject to fading. Multiple measurements will have to be made while moving the field antenna in order to maximize accuracy. Rayleigh fading will contribute uncertainty on the forward and reverse link calculations. Multiple measurements are important in order to develop an accurate picture of the paths being studied. Forward and reverse link measurements should be completed with the same setup at the same locations in order to be accurate. A diplexer or circulator can be used to facilitate the simultaneous transmission and reception of signals using one antenna.

Measuring LTE Reverse Link Path Loss at the eNodeB RxOut Port from a VSG into a unity gain antenna under the DAS antenna. Reverse Link Path Loss =VSG Output – Received RSRP Reverse Link Path Loss= -25dBm – (-78.7dBm-19dB(LNAGain))=72.7dB Note fading caused by multipath.

The VSG can transmit on any frequency so all technologies can be tested with this method.
This 840MHz measurement was injected at a remote coupler. Note the lack of fading. This 1900MHz measurement was transmitted over the air. Note significant fading. Note absence of fading with coupled measurement. Note fading caused by multipath.

Methods of Measuring Path Loss -Forward Link-
Compare known transmitted Pilot and RSRP powers with coupled port or field measurements of received values to determine path loss. CDMA and EVDO Pilot power measurements will require a GPS fix and may not be available. Channel Scanners at coupled ports or with field measurements comparing transmitted and received composite powers. Less accurate and load sensitive. Has the advantage of highlighting transmission failures for periodic maintenance. Tear everything apart and put a CW or Vector Signal Generator on it. Not recommended.

Forward Link Path Measurement : Known –vs- Measured
The difference between the known transmitted and received Pilot and RSRP levels can be measured in the field or at remote coupled ports. Again, these measurements will be compared to reverse link measurements made from the exact same test points at the same approximate time to determine path balance. CDMA Forward Link Path Loss 33dBm Transmitted Pilot – (-39.5dBm Received Pilot)= 72.5dB Forward Link Path Loss EVDO Forward Link Path Loss 41dBm Transmitted Pilot – (-46.5dBm Received Pilot)= 87.5dB Forward Link Path Loss LTE Forward Link Path Loss 21dBm Transmitted RSRP– (-38.1dBm Received RSRP)= 59.1dB Forward Link Path Loss

Yellow Lines and Values Reflect Maximum Hold
Forward Link Path Measurement Process Using a Channel Scanner to measure channel power at the Head End Room using Coupled Ports and comparing the result to field measurements– Measurements must be adjusted to accommodate coupling loss at BTS/eNodeB. Approximates for Ericsson… +75dB 800MHz, +78dB 1900MHz Coupled Ports, +42dB eNodeB Coupler *****MAX HOLD was so that each system could be captured on one screen.***** Yellow Lines and Values Reflect Maximum Hold 35dBm 35 dBm 33dBm 35dBm 41dBm N/A 800MHz EVDO 800MHz CDMA 1900MHz EVDO LTE

Field Measurements with Broadband Antenna
Field measurements can be taken under remote antennas with a broadband antenna or at coupled ports on the far end transmission line. Coupling values per band must also be considered if couplers are used. Over the air measurements will require multiple measurements in order to incorporate the effects of fading. Field Measurements with Broadband Antenna -20dBm -35 dBm -34dBm -43dBm -57dBm Failure Found* N/A 800MHz EVDO 800MHz CDMA 1900MHz EVDO LTE

Forward Link Path Measurement – Channel Power Example
The difference between the Head end and Remote Measurements. These measurements will be compared to reverse link measurements made from the exact same test points using the same test setup and are preferably made at the same time as the forward path measurements. 67dB FL Path Loss 70dB 84dB 55dB

Methods of Measuring Path Loss -Reverse Link-
Apply a CW or VSG (Vector Signal Generator) simulated LTE signal to the remote antenna coupled port and measure the received RSRP and SINR levels at the BTS/eNodeB receivers. Good: Accurate and VSG provides quality (SINR) measurement. Bad: Requires a visit to every remote location. Could take multiple days. Transmit a CW or VSG (Vector Signal Generator) simulated LTE signal below the remote antenna and measure the received RSRP and SINR levels at the BTS/eNodeB receivers. Good: Accurate and provides quality (SINR) measurement. The same setup and location must be used for the forward and reverse measurements in order to evaluate path balance. Tear everything apart and put a CW or Vector Signal Generator on it. Not recommended.

Measurement Method Review
CDMA and EVDO Transmit Gain Adjusts (TGA) are a good approximation of path balance in the field. Note target TGA’s should match the macro system experience. This is a very fast/efficient method but is not exact. LTE does not have TGA but does have a predictable UE transmit profile given an RSRP and a balanced radio path. Deviations from normal behavior would indicate path imbalances. Over the air measurements- Forward and reverse test points must be duplicated so that measurements match. Less accurate than coupled measurements, time consuming. Coupled measurements and injected test signals at the remotes. More accurate than TGA or LTE characterization but requires visits to the head end each remote location. (Typical deployments will take several days.) Invasive CW or VSG measurements for the forward and reverse links. Extremely time consuming and painful but will yield exact results with the right conditions. Recommend this method to people you don’t like.

Q & A Discussion

How about downlink throughput?
It’s all about controlling C/I once your RSRP is <-50dBm. CQI = 15 Throughput degrades almost immediately as the adjacent PCI degrades the C/I while CQI remains at 15. Increasing injected adjacent PCI (noise) Throughput Downlink throughput reduced 49.01% CQI=10

Backup Backup

Potential Impacts of Path Imbalance --Access State--
CDMA, EVDO and LTE accesses use an open loop estimate followed by corrections until a Random Access Response is received. If the initial estimate is much greater than necessary than the initial probe can momentarily raise the noise floor. If the initial estimate is well below the necessary level then additional power corrections will delay access. In the event the corrections do not exceed the necessary level then the customer will not be able to connect. LTE RACH process triggers (Open loop process with corrections) Transition from RRC_IDLE to RRC_CONNECTED. RRC_CONNECTED handing from current to target cell. RRC_CONNECTED but not uplink-synchronized needing to send uplink data, control information, or needing to receive new downlink data. Recovering from radio link failure.

Potential Impacts of Path Imbalances --Connected State--
Handoff - CDMA and EVDO closed loop power control will favor the best reverse link path. As long as the imbalanced sector is in soft handoff with a normal sector, best path will keep power low and maintain reverse link integrity. If mobiles on adjacent sectors are in close proximity to the imbalanced sector but not in soft handoff, then adjacent cell interference is likely. LTE reverse links do not have soft handoff. After handing to an adjacent sector the UE will RACH and closed loop power control will control the UE transmit power. If the UE has to power up significantly, adjacent cells may be affected. Cell edges are designed to have shared RSRP boundaries with similar UE transmit levels. If adjacent cell link budgets are imbalanced then closed loop power control will force UE’s to transmit at higher than expected levels.

**Note that PUCCH and PUSCH power control mechanisms are very similar.
LTE UE uplink closed loop (CL) power control operates around the open loop estimate. The UE adjusts its uplink transmission power based on Transmit Power Control (TPC) commands received from the eNodeB (eNB). **Note that PUCCH and PUSCH power control mechanisms are very similar. PPUSCH =min {Pmax ,10× log10M + P0 +  ×PL +δmcs + f(Δi)} Pmax is the maximum allowed transmit power. M is the number of physical resource blocks (PRB). P0 is cell/UE specific parameter used to control the SNR target and compensate for cell specific noise conditions.  is the path loss compensation factor used for fractional power control. PL is the downlink pathloss estimate based on RSRP measurements and known transmitted reference signal power. δmcs is a cell/UE specific modulation coding scheme value. f(Δi) is the closed loop correction value with a UE specific TPC control. UE specific power headroom reports, Demodulation Reference Signals (DMRS), and Sounding Reference Signals (SRS) are used to estimate uplink channel condition and quality for uplink transmission control. 3GPP “E-UTRA Physical layer procedures”, TS V8.1.0

Instead of raising power, the eNodeB gracefully shifts the UE to a lower Modulation Coding Scheme (MCS) to manage lower SINR. (bits / symbol) Reference – Wikipedia, Channel Capacity for Complex Constellations Example of Downlink MCS Table

Equal Power Handoff Region Between Cells
-Unbalanced CDMA EVDO Systems- Conclusion: DAS System receive levels are susceptible to noise rise from adjacent sector mobile access probes and from adjacent sector mobiles not in soft handoff transmitting at much higher levels. Mobiles in soft handoff will follow TPC commands favoring the lowest transmit levels, somewhat mitigating CDMA/EVDO inter-cell interference. 20 dB less path loss on the reverse link. UNBALANCED BALANCED` ‘User A’ on DAS System CDMA/EVDO Case ‘User A’: Forward Link Pathloss to ‘A’ ≈ 106dB Reverse Link Pathloss to DAS (w/oLNA) ≈ 86dB 800MHz CDMA/EVDO RSSI = -73dBm 800MHz Open Loop Tx = 0dBm Tx Gain Adjust -30dB 800MHz Closed Loop Transmit ≈ -30dBm Channel Power at DAS Rx from ‘A’ ≈ -106dBm Channel Power at DAS Rx from ‘B’ ≈ -96dBm ‘User B’ on Macrocell (or Adjacent DAS) CDMA/EVDO Case ‘User B’: 106dB ≈ Forward Link Path to ‘B’ 106dB ≈ Reverse Link Path to Macrocell (w/oLNA) -73dBm = 800MHz CDMA/EVDO RSSI 0dBm = 800MHz Open Loop Tx -10dB Typical Tx Gain Adjust -10dBm ≈ 800MHz Closed Loop Transmit -106dBm ≈ Channel Power at Macrocell from ‘B’ -136dBm ≈ -30dBm - 106dB =Rx Channel Power from ’A’

Ericsson eNodeB Rx Out Port Characterization
Two port gain test using a 40dB coupler on the eNB RF port to determine Rx OUT gain in receive path. The coupler was not calibrated into the test setup so the signal is first attenuated by 40dB and then amplified by the eNB to achieve an average of approximately -21dB at Rx I/O. Rx eNB gain is -21dB – (-40dB) or 19dB. Net Rx OUT gain is approx. +19dB

Path Balance on Distributed Antenna Systems Presentation by Dennis McColl - April 2nd, 2013 PUSCH PUCCH.

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Path Balance on Distributed Antenna Systems Presentation by Dennis McColl - April 2nd, 2013 PUSCH PUCCH.

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