# Joint Transmission with Dummy Symbols for Dynamic TDD in Ultra-Dense Deployments

## TL;DR

This paper proposes a joint transmission scheme with dummy symbols to mitigate interference in dynamic TDD ultra-dense networks, enhancing uplink and downlink performance especially at low to medium utilization levels.

## Contribution

It introduces a novel joint transmission method using dummy symbols to nullify BS-to-BS interference in dynamic TDD ultra-dense deployments.

## Key findings

- Significant uplink and downlink performance gains at low and medium utilization.
- The proposed dummy symbol scheme effectively reduces interference.
- Trade-offs between uplink and downlink performance can be managed by adjusting participating BSs.

## Abstract

Dynamic time-division duplexing (TDD) is considered a promising solution to deal with fast-varying traffic often found in ultra-densely deployed networks. At the same time, it generates more interference which may degrade the performance of some user equipment (UE). When base station (BS) utilization is low, some BSs may not have an UE to serve. Rather than going into sleep mode, the idle BSs can help nearby UEs using joint transmission. To deal with BS-to-BS interference, we propose using joint transmission with dummy symbols where uplink BSs serving uplink UEs participate in the precoding. Since BSs are not aware of the uplink symbols beforehand, any symbols with zero power can be transmitted instead to null the BS-to-BS interference. Numerical results show significant performance gains for uplink and downlink at low and medium utilization. By varying the number of participating uplink BSs in the precoding, we also show that it is possible to successfully trade performance in the two directions.