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Compensating Synchronization Accuracy to Reference Timing Source

IP.com Disclosure Number: IPCOM000240308D
Publication Date: 2015-Jan-21
Document File: 4 page(s) / 229K

Publishing Venue

The IP.com Prior Art Database

Abstract

In Long Term Evolution (LTE) networks synchronization is needed to ensure network quality and availability. Synchronization here refers to the technique applied to ensure that radios in target LTE base station are operating within the performance parameters defined by the appropriate 3rd Generation Partners Project (3GPP) standard. Synchronization is achieved by delivering a specifically formatted clock signal or signals to the basestation’s radio circuitry. These signals in turn are used to generate the modulation method’s RF air interface frequency/phase components. The synchronization reference source can be GPS signal, PTP generated timing or timing retrieved from listening to nearby networks (Network Listening Mode / NLM).

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Compensating Synchronization Accuracy to Reference Timing Source

Abstract

In Long Term Evolution (LTE) networks synchronization is needed to ensure network quality and availability. Synchronization here refers to the technique applied to ensure that radios in target LTE base station are operating within the performance parameters defined by the appropriate 3rd Generation Partners Project (3GPP) standard. Synchronization is achieved by delivering a specifically formatted clock signal or signals to the basestation’s radio circuitry. These signals in turn are used to generate the modulation method’s RF air interface frequency/phase components. The synchronization reference source can be GPS signal, PTP generated timing or timing retrieved from listening to nearby networks (Network Listening Mode / NLM).

Problem Description

One method to synchronize is to use two step process  to synchronize to reference timing. In first step, the reference timing (GPS) is synchronized to a constant frequency clock (reference clock). In second stop, the timing information is transferred from reference clock to data clock (cellular IQ data). In JESD207 systems, the data clock frequency is usually equal to baseband sampling frequency (or chip clock).

As a simple double flop synchronizer introduces inaccuracy of 1 clock period, the total synchronization inaccuracy in encountered in synchronization scheme is 1 chip clock period + 1 reference clock period.

At lower LTE bandwidths (e.g. 1.4MHz and 3MHz), the synchronization inaccuracy is in order of the synchronization accuracy parameters defined in LTE standards. This comparable synchronization inaccuracy affects robustness of the network in negative way. For example, for a 19.2MHz reference clock and 1.4MHz LTE bandwidth, the synchronization inaccuracy is:

52ns (reference clock) + 530.833ns (chip clock).

This inaccuracy is comparable to synchronization requirements of LTE spec:

Synchronization Requirements for Different Types of LTE

Application

Phase  Alignment Requirement

LTE(FDD)

NA

LTE(TDD)

±1.5µs

LTE MBSFN

-1 to 32µs

LTE-A CoMP

±500ns (±0.5µs)

LTE (residential)

None

Solution Description

The solution describes a hardware assisted method for software to compensate for the inaccuracy.

The solution adds logic in hardware to measure delay between reference timing source pulse and the “ch...