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Adjacent channel interference analysis

© 2011 Real Wireless Ltd.

Adjacent channel interference scenarios

© 2010 Real Wireless Ltd. 2

Study questions

1.23 What would be the impact of interference from adjacent WiMAX or TD-LTE

networks in the unpaired band on the operation of a low-power network?

1.24 What would be the impact of interference radar emissions in the 2700 to 2900

MHz band on the operation of a low-power network?

1.25 What other technical conditions might be needed to manage any

interference?


Adjacent channel interference scenarios(Study question 1.23 and 1.24)

UPLINK TDD DOWNLINK RADAR

UL low-power block

DL low-power block

Adjacent channel interference from potential high power TDD macros

Adjacent channel interference from S-band radar

2.6 GHz band plan with adjacent interference bands


Adjacent channel interference scenarios(Study question 1.23)

High power edge of cell

WiMAX or TD-LTE UE

Interference

Indoor user on edge of

coverage

Short distance and/or good LOS

Uplink case

Short distance and/or good

LOS

Edge of coverage

UE

WiMAX or TD-LTE BS

Interference

Downlink case

WiMAX or TD-LTE BS

Interference


Indoor user on edge of

coverage

Adjacent channel interference scenarios(Study question 1.23 – Scenario 18)

Short distance and/or good LOS

Uplink case

Short distance and/or good

LOS

Edge of coverage

UE

WiMAX or TD-LTE BS

Interference

Downlink case

WiMAX or TD-LTE BS

Interference

Assume uplink case only is relevant as sufficient frequency separation between the TDD band and FDD DL low power band

Interference

As the UE transmits a relatively small proportion of the time interference from the WiMAX UE is less significant than from the WiMAX BS (see CEPT report 19)

However, interference from indoor WiMAX access points to indoor LTE FDD access points is a concern and needs examining (see next slide)


WiMAX or TD-LTE UE


Adjacent channel interference scenarios(Study question 1.23 - Scenario 18)

Concern amongst operators about adjacent channel interference between WiMAX and LTE FDD access points deployed in the same shopping centre. Need to interpret the CEPT study (report 19) on macro to macro interference between TDD and FDD systems to low power access points.

LTE FDD access points

WiMAX TDD access points


WiMAX or TD-LTE UE Value Units

Local eNBtx power

0 to 24 dBm

Antennagain

3 dBi

Bandwidth 20 MHz

ACLR 45 dB

Propagation model

free space path loss

ACS 43.5 dB

NF 8 dB

Separation distance between a low power TDD AP and a low power FDD AP (20 MHz)


With 5 dB less interference

between 20% and 50%

degradation the separation

distance drops from 80m to

30m

Separation distance could be within 20m between a TDD and FDD access point at 12 dBmtransmit power

for a public indoor

deployment

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Transmit output power (dBm)

Target througput 37 Mbps

Tput 20% degradation


Separation distance between a low power TDD AP and a low power FDD AP (10 MHz)


With 5 dB less interference

between 20% and 50%

degradation the separation

distance drops from 80m to

30m.

Separation distance could be below 20m

between a TDD and FDD access point at 12 dBmtransmit power

for a public indoor

deployment

Separation distance is slightly greater (30m) for a 10 MHz bandwidth when at max power

compared to 20 MHz bandwidth at max power since the transmit power is constant with BW so for 20 MHz PSD is less than a 10

MHz channel so the range drops slightly

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Target throughput 18.5 Mbps



Separation distance between a macro TDD BS and a low power FDD AP (20 MHz)


For a macro at max power there is

approx 1km difference between

20% degradation and 50%

degradation. This is due to the lower target SNR

resulting in a larger degradation in

throughput

This scenario should take into

account the practical

separation distance

between an indoor access point and an

outdoor macro.

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Target throughput 37 Mbps



Separation distance between a macro TDD BS and a low power FDD AP (10 MHz)


For macro at max power there is a 2km discrepancy

between 20% degradation and

50% degradation. This is due to the lower target SNR

resulting in a larger degradation in

throughput

Separation distances up to 3.5km for a TDD

macro at max transmit power for a 20% Tput

degradation0.0

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Target throughput 18.5 Mbps



Conclusions from ACI TDD (WiMAX or TD-LTE) into LP FDD


• There is a requirement for a separation distance between indoor low- power TDD deployments and low power FDD deployments ranging between 20m to 80m for a range of increasing transmit powers. This means TDD operators in the adjacent block to the low power uplink block will require some coordination when deploying in the same indoor public area

• A slightly wider separation distance is required for a 10 MHz compared to a 20 MHz channel. This is due to a constant transmit power being spread over a wider bandwidth in the case of 20MHz so the power spectral density is less than in the 10MHz case.

• The separation distance between a TDD macro and an FDD low power access point can be up to 2.2km at the maximum transmit power. Further analysis for example taking into account difference in antenna heights may also vary the separation distance i.e. Tall TDD macro mast may cause interference to low-power access points at a greater distance (see study question 1.18)

• Based on the findings from the study questions addressing the coverage scenarios using 18 dBmEIRP to achieve satisfactory coverage for an indoor deployment would require a separation distance of about 40m which can be considered reasonable without coordination

Previous studies on interference between TDD and FDD systems in the 2.6 GHz band


• CEPT Report 019 - Draft Report from CEPT to the European Commission in response to the Mandate to develop least restrictive technical conditions for frequency bands addressed in the context of WAPECS– Report provides a methodology for least technical restrictions to protect adjacent TDD

services. -45 dBm/MHz block edge mask should be used for base stations and -19 dBm/MHz should be used for UE’s. In block transmit powers are given with 61 dBm/5 MHz EIRP for unrestricted BS’s and 25 dBm/5 MHz for restricted BS’s

• CEPT Report 119 – Coexistence between mobile systems in the 2.6 ghz frequency band at the fdd/tdd boundary– Includes results for separation distances for BS-BS interference e.g. 1km with up to 10 MHz

carrier separation without mitigation techniques applied

• ECC Report 045 - Sharing and adjacent band compatibility Between UMTS/IMT-2000 in the band 2500-2690 MHz and other Services – This report focuses on the adjacent services to the 2.6 GHz band such as MSS, RAS and MMDS.

This was not directly relevant to the present study

• ECC Report 113 - derivation of a Block Edge Mask (BEM) for terminal stations IN THE 2.6 GHz FREQUENCY BAND (2500-2690 MHz)– This report had a specific focus on terminal station to terminal station interference and

deriving the block edge masks which includes the methodology and protection levels. Parts of this report were relevant to the present study


Adjacent channel interference from S-band radar into indoor femtonetwork, UE on limit of coverage is most critical

Adjacent channel interference scenarios(Study question 1.24 outdoor)

Pulsed wideband radar DL interference

Interference

Front lobe

Back lobes

Value Units

Radar Txpower

91.2 dBm

Antenna gain (main beam)

28 dBi

Antenna gain (side lobe)

-2 dBi

HP Beamwidth

1.5 Deg

ACIR 26.8 dB

Propagation model

ITU-R P 1411

Duty cycle 1.7 µS

PRF 1 kHz

BPL 14 dB

Radar antenna height

12 m

Mobile height

1.5 m

Separation distance between an FDD UE and radar – Outdoor


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Thro

ughp

ut (M

bps)

Separation distance (km)

Separation distance of FDD UE from radar - Main beamMax throughput 82 Mbps

ITU-R P1411

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Separation distance of FDD UE from radar - Side lobes Max throughput 82 Mbps

ITU-R P 1411

When in the main beam the peak pulse

power occurs for several micro seconds which is considered a negligible interference

effect

The antenna vertical pattern attenuation is

max close to the radar and reduces as

distance increases.

However, the pathloss

dominates due to the large

power from the radar

The UE’s will experience

interference power from within the

sidelobes of the radar for 99.6% of the time.

Outdoor effects are more severe than indoor due to no

building penetration loss attenuation .


Adjacent channel interference from S-band radar into indoor femtonetwork. Downlink to UE is most critical case as assume sufficient separation between S band radar and FDD UL band.

Adjacent channel interference scenarios(Study question 1.24 indoor)

Interference

Pulsed wideband radar DL

interference

Front lobe

Back lobes

Separation distance between an FDD UE and radar – Indoor


When in the main beam the peak pulse

power occurs for several micro seconds

which will cause a negligible effect in the

UE receiverSeparation distance from a radar takes into

account the variation in

antenna pattern attenuation

with distance.

The UE’s will experience

interference power from within the

sidelobes of the radar for 99.6% of the time.

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Separation distance of FDD UE from radar - Main beamMax throughput 82 Mbps

ITU-R P 1411

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Separation Distance (km)

Separation distance of FDD UE from radar - Side lobes Max throughput 82 Mbps

ITU-R P 1411

The impact to indoor UE’s is better compared to outdoors with UE’s

ability to achieve a reasonable Tput at

distances under 5km

Conclusions from radar interference into FDD UE


• Interference from radar emissions consist of peak power when the UE is in the main beam of the radar and the mean power when the UE is in the side/back lobes of the radar. This means there is a difference in the interference due to the attenuation of 30 dB of the signal when in the side lobes.

• The peak interference also occurs for very short pulse duration, in this case 1.7 µS (Magnetron) with a pulse repetition frequency of 1 kHz. This means a duty cycle is 0.17% which is considered negligible to the UE receiver as the signal appears as a short pulse and not continuous interference

• The horizontal antenna pattern beamwidth is 1.5 degrees which equates to (1.5/360) 0.4% of the time the UE appears in the main beam. For 99.6% of the time the UE appears in the side lobes. The mean (side lobe power) interference appears as a continuous signal at the UE receiver due to the swept nature of the signal and the rotation of the antenna.

• The degradation rate at the receiver is unknown without further measurement of the cause to the individual Resource Blocks. It should be noted that for a 1.7 µS pulse duration every 1ms will affect the allocated resource blocks but it is not likely to be as severe as in the co-channel environment.

• The resultant separation distance that should be considered in this scenario are those from side lobe power scenario as the dominant effects of the interference are generated within the side lobes .

• Where circumstances may be improved from the scenario investigated for this study include:– Radar frequency higher up the S-band which will improve the adjacent channel Out of band suppression

level – An increased radar height may improve the situation as the vertical pattern beamwidth reaches the horizon

in shorter distance compared to decreased radar height– Lower peak power, this scenario used the highest possible licensed peak power which is not necessarily the

case at every airport. Some airports will transmit at peak power’s 3-10 dB lower that the peak used in this scenario

Previous studies on interference from radar to 2.6 GHz band


• WiMAX Forum – Roke Manor – Separation distance for ATC 2.7 GHz radars into

WiMAX BS and UE was 104.8 km and 75.4 km in the main beam and 14.3km and 3.9km in the side lobes (outdoors) respectively

– These results correspond reasonably well with the separation distances calculated from our scenario. Main beam: 60 km (max Tput) Sidelobes: 10km (max Tput) UE only

– This study used free space path loss with exponent of 3 + 10 dB shadowing. Compared to ITU-R P 1411 for our scenario which is good for LOS situations and capture the diffraction effects

Previous studies on interference from radar to 2.6 GHz band


• ERA Study for Ofcom– Carrier to Interference calculations showed correlation of the

peak and average power between the main beam gain and sidelobes gain

– For the majority of ATC radars the out of band emission measurements were below -40 dBm/MHz, some radars were -70 dBm/MHz whose carrier frequency was higher up the S-band

– Between 600m and 800m there was no measurable interference from the radar in one full rotation into a UMTS handset

– This may not be the case for an OFDMA LTE UE as the pulse repetition frequency can impact individual resource blocks within the 1ms timeframe

– Radiated interference measurements were of the BER within a reference UMTS channel based on a data rate of 12.2 kbps. The reference channel measurements are likely to be different for LTE systems

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Adjacent channel interference analysis - · PDF fileAdjacent channel interference analysis ... LTE BS Interference ... Adjacent channel interference from S-band radar into indoor femto