LTE TDD Coexistence_ZTE

Adjacent Channel Interference Analysis for 2.5MHz Guard Band in TD-LTE network

Case study for Maharashtra


Technical Description

Version Date Author Approved By Remarks

V1.00 2011-07-17 ZTE Bharti Airtel Not open to the Third Party

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© 2023 ZTE Corporation. All rights reserved.

ZTE CONFIDENTIAL: This document contains proprietary information of ZTE and is not to be disclosed or used without the prior written permission of ZTE.

Due to update and improvement of ZTE products and technologies, information in this document is subjected to change without notice.


TABLE OF CONTENTS

1 Introduction........................................................................................................11.1 Spectrum Allocation.............................................................................................11.2 Worst Interfering case.........................................................................................1

2 Common Types of Interference.......................................................................12.1 Transmitter Noise (Spurious emission)...............................................................32.1.1 TD-LTE Tx Characteristics..................................................................................32.2 Receiver Blocking (Desensitization)....................................................................42.2.1 Reliance Receiver Blocking Characteristics........................................................52.3 Inter-modulation (IM)...........................................................................................5

3 Isolation Analysis..............................................................................................63.1 Receiver Blocking................................................................................................63.2 Transmitter Noise................................................................................................63.2.1 Reliance Rx Sensitivity........................................................................................63.2.2 Airtel Tx Filter......................................................................................................73.3 Inter-modulations.................................................................................................83.3.1 TX Inter-Modulation Products..............................................................................83.3.2 RX Inter-Modulation Products.............................................................................8

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FIGURES

Figure 1 Interference from Transmitter to Receiver..................................................................3

Figure 2 Spectrum Emission Mask for TD-LTE eNB Transmitter..............................................4

Figure 3 Rx Sensitivity Calculation............................................................................................7

Figure 4 IM3 and IM5................................................................................................................8

TABLES

Table 1 Spectrum Emission Mask for TD-LTE eNB Transmitter...............................................3

Table 2 Adjacent Channel Selectivity for TD-LTE eNB Receiver..............................................5



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1 IntroductionThis document describes adjacent channel interference between two TD-LTE networks in Indian western state Maharashtra, one belongs to Bharti Airtel, the other belongs to Reliance. Frequency guard band for isolation is only 2.5MHz.

This note describes common type of potential interference to Reliance systems and analyses the isolation requirements to avoid any such interference.

Please also note the minimum isolation required is computed as per the strict criteria defined in TD-LTE standards. The minimum isolation required is independent to TD-LTE eNB vendor.

1.1 Spectrum Allocation

Bharti Airtel TD-LTE frequency band is 2305MHz ~ 2325MHz in Maharashtra.

Reliance TD-LTE frequency band is 2307.5MHz ~ 2347.5MHz in Maharashtra.

This document analyses the filter feasibility and requirements for avoiding possibility of potential interference from Airtel TD-LTE Tx to Reliance TD-LTE Rx, and vice versa from Reliance TD-LTE Tx to Airtel TD-LTE Rx.

1.2 Worst Interfering case

Following 2 cases would be considered in this document from transmitter to receiver:

Case 1: 2.5MHz guard band between Airtel eNB downlink transmitter to Reliance eNB uplink receiver.

Case 2: 2.5MHz guard band between Reliance downlink transmitter to Airtel eNB uplink receiver.

Case 2 is actually the same as case 1.

In this document, case 1 will be analyzed in detail.

2 Common Types of InterferenceThe spectral emissions from an eNodeB are unfortunately not strictly band-limited within the desired carrier bandwidth. This is due to practical limitations on filter technology and on the linearity of amplification.



All sources of attenuation of the signal between transmitter and receiver due to phenomena such as propagation, antenna radiation patterns and cable losses are denoted by a single ‘coupling loss’.

In the region marked ‘A’, energy from the transmitter falls directly within the desired passband of the receiver, while in region ‘B’ the non-ideal characteristic of the receiver collects energy from inside the passband of the transmitter. In region ‘C’ transmitted energy falling outside both the transmit and

receive passbands is collected by the non-ideal receiver characteristic. The aggregated effects of regions A, B and C represent the total unwanted energy from the interfering transmitter that is captured by the receiver.

Interference arising from regions A and B is controlled by performance requirements imposed on the transmitting and receiving devices respectively, while in region C both transmitter performance and receiver performance have an impact. The interference effects are generally small for large frequency separations (such as in the case of FDD), and when there is a large coupling loss between the interfering transmitter and a ‘victim’ receiver, as is the case when there is a large physical separation between the two.

Naturally, the interference effects are most pronounced when the transmitter and receiver operate on adjacent carrier frequencies (excepting the co-channel case) and with low coupling loss (e.g. due to small spatial separation). These worst-case adjacent-channel scenarios form the basis upon which key requirements for transmitter and receiver are generally set.

The overall ‘leakage’ (whether at the transmit side or the receive side) from a transmission on one carrier into a receiver operating on an adjacent carrier is described by the Adjacent Channel Interference Ratio (ACIR), which is derived from the transmitter’s Adjacent Channel Leakage Ratio (ACLR) and the receiver’s Adjacent Channel Selectivity (ACS). It is worth noting that it is often the case that the ACIR is dominated by either the ACS or the ACLR.

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Figure 1 Interference from Transmitter to Receiver

2.1 Transmitter Noise (Spurious emission)

This interference occurs when the noise power generated by the down-link (DL) transmitter of one network falls in the up-link (UL) band of the second network.

2.1.1 TD-LTE Tx Characteristics

For the TD-LTE system operating at Ptx = 46 dBm (40W) in 20 MHz, noise outside the channel as defined by 3GPP36.104 is as follows:

Table 1 Spectrum Emission Mask for TD-LTE eNB Transmitter



Figure 2 Spectrum Emission Mask for TD-LTE eNB Transmitter

Frequency offset = 2.5MHz, Pn = -7dBm-7/5*( 2.5-0.05) = -10.43 dBm in 100 KHz = -0.43 dBm in 1 MHz

2.2 Receiver Blocking (Desensitization)

The result of the down link carrier from one network, at the receiver input of a second network, being strong enough to cause the receiver to compress - even if the signal is not in the up link band.

This is the most difficult specification to meet as the only way to reduce the level of this signal is to provide good antenna isolation, or a filter at the Reliance UL input.

In the given case, filtering at the Reliance receive will help to eliminate Rx blocking, but may not be under the control of Bharti Airtel.

At the same time, filtering at Airtel site will not help eliminate Reliance receiver blocking because high power in Airtel pass band (20 Mhz) can potentially cause Reliance receiver blocking. Filtering only attenuates Airtel spurious transmission.



2.2.1 Reliance Receiver Blocking Characteristics

The maximum power level of an unwanted signal (P) at the receiver input for each system as per 3GPP36.104, is as follows

Table 2 Adjacent Channel Selectivity for TD-LTE eNB Receiver

E-UTRAchannel

bandwidth [MHz]

Wanted signal mean power

[dBm]

Interfering signal mean power [dBm]

Interfering signal centre frequency offset from the

channel edge of the wanted signal

[MHz]

Type of interfering signal

1.4 PREFSENS + 11dB* -52 0.70251.4MHz E-UTRA

signal3 PREFSENS + 8dB* -52 1.5075 3MHz E-UTRA signal5 PREFSENS + 6dB* -52 2.5025 5MHz E-UTRA signal

10 PREFSENS + 6dB* -52 2.5075 5MHz E-UTRA signal15 PREFSENS + 6dB* -52 2.5125 5MHz E-UTRA signal20 PREFSENS + 6dB* -52 2.5025 5MHz E-UTRA signal

TD-LTE systems (for Fo - F = 2.5 MHz), P = -52-6 = -58 dBm

Note that this requirement is on total power of the unwanted transmit signal, and is not limited to, for example, the transmit power in 100 KHz.

2.3 Inter-modulation (IM)

IM products are created when two or more frequencies mix in non-linear devices in TX or Rx path. IM products of order n are sums and differences in n terms of the original frequencies.

TX IM -- created at the TX BTS through the mixing of carriers in the same power amplifier, combiners, diplexers, connectors or antennas.

Rx IM -- the result of two TX carriers from one network creating inter-modulation products, in the LNA of a second network, that land in the UL band of the second network at levels higher than the receive system sensitivity. Since the IM products can be quite high, we will consider both 3rd and 5th order products.



3 Isolation Analysis

3.1 Receiver Blocking

As discussed in section 2.2, the Reliance receiver blocking threshold requirement on total unwanted power radiated, for Fo - F = 2.5 MHz, is -58 dBm. Hence,

-58 dBm > 46 dBm (Airtel Max. Tx Pwr) - isolation (dB)

Note that as discussed in the previous section, this isolation to eliminate receiver blocking cannot be provided by any filtering at Airtel transmit.

Hence the two ways to achieve this isolation are: (1) By physical separation between Airtel and Reliance antennas. (2) By filtering at Reliance.

Total isolation required for 2.5 MHz guard band is 46 + 58 104 dB.

For co-locate case that Airtel and Reliance deploy their TD-LTE antennas in the same site, the antenna isolation is 30dB. Reliance receiver filter must can suppress 74dB (104-30).

If no Reliance receiver filter suppression, antenna isolation is 104dB, which needs 1511m horizontal ( or 10m vertical) inter-site distance. It is very difficult for eNB deployment.

3.2 Transmitter Noise

The spurious, out-of-band energy radiated by the Airtel eNB has been discussed in Section 2.1.

For the worst interference scenario considered in this study the TD-LTE spurious energy is

-0.43 dBm in 1MHz (Case 1)

3.2.1 Reliance Rx Sensitivity

For the Airtel carrier not to interfere with the Reliance system, the Tx noise power at the Reliance receiver input must be less than -116 dBm in a 1MHz bandwidth.

-116dBm/MHz is from Airtel passband noise requirement. It is combined with Reliance thermal noise requirement -109dBm/MHz, then get (-109+0.8) dBm/MHz.



Figure 3 Rx Sensitivity Calculation

3.2.2 Airtel Tx Filter

To achieve -116 dBm in a 1MHz bandwidth at Reliance receive, filtering at the Airtel transmit (FR) is required in addition to 30 dB antenna isolation for co-locate deployment.

CASE 1: 2.5MHz Guard Band

-116 dBm = (-0.43) dBm - Isolation total ===> Isolation Total = 116 dB

However 30 dB isolation is achieved through physical separation of antennas for co-locate deployment. Total isolation is a combination of isolation achieved by physical separation and by filtering at Airtel transmits.

Hence, Required filtering at Airtel TX (FR)

-116 dBm = ( -0.43)dBm - 30 dB – FR ===> FR = 86 dB



3.3 Inter-modulations

Figure 4 IM3 and IM5

For Reliance receiver 20MHz carrier with only 2.5MHz guard band near Airtel, 17.5MHz channel receives 3rd order IM and another 2.5MHz channel receives 5rd order IM.

3.3.1 TX Inter-Modulation Products

The analysis shows that two homogenic TD-LTE carriers do not generate significant transmit inter-modulation products.

Spectrum emission mask in section 2.1 has contained Tx IM consideration. As a result, this type of interference is not an issue.

3.3.2 RX Inter-Modulation Products

The Reliance receiver 3rd order IM will now fall in band thus requiring very good IM performance, but receive blocking requirement in section 2.2 has included Rx IM factors. So the 3rd order Rx IM becomes a negligible issue.


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