Engineers’ Roundtable: Spectrum Efficiency

In a previous blog post, some of TeleWorld’s top engineers discussed the challenges mobile operators face in virtualizing their networks.

Today, our experts discuss how operators can address “spectrum crunch” and get greater efficiency out of the spectrum they currently have.

Scott Robertson

Network densification has to play a key role in a broader strategy of maximizing spectrum efficiency. We’re seeing this paradigm shift happening today, as many of the world’s largest wireless operators densify their high-traffic markets through a mixture of small cells and outdoor distributed antenna systems. Bringing the RF closer to end users will allow for more efficient use of both existing and newly deployed spectrum, while maximizing customers’ broadband experience.

Additionally, as cloud-based and digital platforms become more ubiquitous, dynamic capacity management strategies can be implemented to shape traffic more efficiently, maximizing RF resource utilization and ensuring capacity is available for consumers where and when they need it.

Mathew Dooley

Adding more spectrum through auctions and acquisitions certainly will help add more capacity, but it also increases the growing complexity of today’s networks. Lower frequency bands have great propagation characteristics, but this creates SINR challenges. High frequency bands have great SINR characteristics with the obvious coverage challenges. While spectrum helps, densification is still clearly needed; but how do we incorporate the new spectrum bands into existing cell plans and overcome these challenges?

First, you have to understand the problem:   What’s the issue leading to the new spectrum/cell need? Is it the number of users; poor MCS leading to low spectral efficiency, coverage, or operational issues; or some combination?

As Scott mentioned, RAN Cloud, SON, and other dynamic traffic shaping tools will help, but good installation practices, design, and testing strategies are critical to moving networks forward.

Mohammad Baig

I feel that ongoing maintenance and optimization are crucial. Networks are driven by parameter settings, so ensuring that devices are directed to the desired band and frequency at the proper time is paramount. RAN features must be utilized properly, specifically those that manage and shift traffic across bands using a measured load on the network. Our experience has shown mismatches in terms of traffic carried across bands and modes, which results in inefficiencies.

Spectrum re-harvesting helps. Many operators have shifted substantial traffic over to LTE and off of legacy technologies, allowing the occupied spectrum to be re-harvested for use with 4G LTE.

JongHak Jung

Carrier aggregation is one of the key items for spectral efficiency enhancements. This should be considered not only in single-band CA, but also across the multiple bands — 700, 800, AWS, PCS, 2.4 (unlicensed) and 2.5 GHz and beyond.

The across-band CA can also benefit the coverage increase if several factors are considered. First, macro coverage is mostly UL-limited due to UE power limits. And lower spectrum propagates further compared to higher spectrum in physical links. So, if two distanced spectrum such as 700 vs. AWS CA is capable, the UE of the AWS band can be used for 700 UL, while DL transactions can be in AWS with higher bandwidth, which results in wider coverage than AWS UL. This would also relieve the load imbalance between or among the bands for the sites.

One challenge is the inter-sector CA for the across-band CA when coverage of the higher spectrum is not contiguous, while lower spectrum is. In such cases, the data transaction will be seamless regardless of coverage differences between the two spectrum bands.

Bhupinder Mann

All the latest technologies are pretty much using frequency reuse at N=1. In other words, all sectors can use the same operating frequency. But in reality you can never achieve N=1 due to the cell edge interference from neighboring cells, and the techniques to mitigate these issues are limited.

This drives the requirement for a better-optimized network to improve the effectiveness of N=1, but the strategy needs to be different from CDMA-based technologies, like CDMA and UMTS vs. LTE, which is OFDMA-based. Operators need to understand this, especially the ones operating both 4G and 3G networks.

Bits/Hz is a simple way to define spectral efficiency. The newest techniques – ICIC, CA, etc. – have to be utilized and optimized, along with limiting RF overlaps, spills, and overshoots at air interface, etc. This approach needs to be complemented with small cells and other solutions, such as Wi-Fi, to maximize spectral efficiencies.

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