A Wireless-Wireline Physically Converged Architecture: Introducing Cellular Subscriber Lines

As customer demand for high-bandwidth services increases, providers look for ways to maximize existing infrastructure and manage costs. ASSIA is proud to be at the forefront of an innovative approach to solve this challenge: CSL (Cellular Subscriber Lines). CSL, as detailed in this paper published for IEEE, is a ground-breaking new concept for greatly extending radio coverage and data rates. CSL re-uses existing wireless-wireline architecture—copper phone, Ethernet, coaxial cable, and other wireline connections—to deploy numerous wireless small cells in an economical manner. The value of this approach is improved bandwidth at a much lower cost.

How CSL Works

CSL leverages existing cabling in a very low-cost architecture. As shown in the figure below, a single BaseBand Unit (BBU) communicates over existing cabling to many remote radio heads. The CSL-IFs down-convert the wireless baseband unit’s (BBU’s) signals to the appropriate frequencies for transmission through the wireline connection, with up-conversion at the CSL-RF. The same process also runs in reverse (with up-conversion at the CSL-RF) to provide bi-directional transmission. Complex modulation, coding, signal processing, MIMO, and other functions are performed at the BBU. The CSL-RF remote radio head (RRH) only needs to perform simple analog frequency conversion and amplification, thereby allowing a very low-cost, small and simple radio head. Further, communication over the wire is exceedingly simple, using existing cabling, with no need to run new fiber, and no costly optical to electrical (O2E) conversion.


Identical to 4G LTE and 5G NR, CSL modulates OFDM (Orthogonal Frequency Division Multiplexing) signals, thereby providing complete interoperability with existing 4G/5G systems and handsets. The authors show that these OFDM signals are advantageously also nearly optimal for wireline transmission, when sent at the proper frequencies. For more details, refer to the IEEE paper to learn how cellular’s OFDM systems can be used to implement near-optimal DSL performance with the wireless signals.

Because radio head/base stations are simply-constructed and low-power, they cost less to deploy. When feeding many distributed small cells, these cost-savings could be significant.

Cost-Effective Wireless Deployment

With CSL, the baseband wireless link now includes the metallic baseband/IF signals, which has less attenuation than the same-length wireless link. Furthermore, several spatial streams can be multiplexed on single wire, allowing low-cost deployment of enhanced MIMO (Multi-Input, Multi-Output) systems for increased wireless performance.

Further, the electrical power that existing copper wire may deliver to the home could also energize the CSL-RF, solving the thorny problem of powering numerous small cells. Similarly, this architecture accommodates Wi-Fi systems, which is well-suited to enterprise deployments where Ethernet cable is present. The super-heterodyning concept of IF and RF can enable very low-cost proliferation and allow cloud-based control to enhance existing standardized infrastructure.


CSL systems may well provide an excellent solution to the increasing need for more cost-effective wireless deployment so that the promise of a highly connected wireless future can advance with much less economic risk. CSL can enable the 5G vision

Massive Bandwidth Lift

As consumers demand better wireless quality in- and out-of-home, quality of service is critical but potentially costly. CSL would address this increasing demand with less economic risk. Cellular-wireless (or Wi-Fi-wireless), MCS, and MIMO methods’ re-use on copper costs less, uses more existing infrastructure, and improves wireless residential networks’ profitability.

Further, and possibly most dramatic, is the spectral efficiency, increase in effective speeds, and low latency provided by the ability of CSL to provide a cost-effective massive decrease in cell radius.

Data Rates (down plus up)

In the example above, an approximate decrease by a factor of 5 in cell radius provides over a factor of 25 increase in cellular reuse, with a consequent factor of 25 increase in effective bandwidth.

In summary, CSL is a dramatic and less expensive way to put a cell base station at every house so every customer gets a massive bandwidth increase for their mobile devices. By using their existing copper wiring (pair cable or coax), providers avoid the need to deploy a lot of fiber to the home.

While an exceptional solution for areas with wireline access built out 20-50 years ago, CSL is also a disruptive concept for the many countries that have already started to invest in getting fiber to every home.

For more information on CSL, contact the ASSIA sales team.