In US FCC and in Europe ECC have outlined the rules for TV-band secondary use. In this paper we apply those rules and compute how much white space is available in Finland. The results are expressed in terms of available secondary channels and secondary system capacity. As a secondary system we use cellular networks with different cell sizes. Unfortunately, the current secondary spectrum usage rules do not protect the TV receivers sufficiently well. Even if each individual secondary transmitter obey them, together their aggregate interference can still disrupt the TV reception. We compute how much aggregate interference a secondary network generates if the network is designed either by FCC or ECC rules. We discover that only for a low secondary transmitters' density, the TV reception will not be disturbed. We can conclude that current white space usage rules are not adequate for protecting the TV receivers. There is a need to develop constraints that consider not only secondary transmission powers but also transmitters' density.

Dynamic time-division duplexing (TDD) enables adjustments of uplink (UL) and downlink (DL) resources flexibly according to the instantaneous traffic load. Long-Term Evolution (LTE) systems can be implemented in TDD mode (TD-LTE). However, the dynamic change of a TDD configuration has not been well supported and investigated. In large macro cells, the high transmit power of base stations (BSs) easily blocks the weaker user equipment's (UE) UL signal (called the UL-DL interference); and therefore, neighboring cells usually operate with the same TDD configuration. In small cells, such as femtocells, the BS and UE transmission powers are in the same order and the system can afford to have overlapping UL-DL subframes. In addition, when DL load is light, the BS transmits empty DL subframes with only a reference signal (RS). In this paper, we measured the interference caused by DL RS. This interference is not negligible; and therefore, it is beneficial to reduce the amount of DL subframes by switching lightly loaded BSs to UL-heavy subframe configuration. We illustrate with simulations that this can improve system efficiency. Changing the subframe configuration dynamically has a switching-related cost. Frequent switching between subframe configurations can actually decrease throughput. We describe conditions where configuration change is beneficial. We also propose an algorithm that decreases the switching overhead and improves the ability to adapt to varying loads.

Cloud radio access networks use servers that are connected to Remote Radio Heads (RRH). Base station (BS) implementation with this concept is challenging. The strict realtime nature of baseband (BB) processing seems to rule out usage of General Purpose Processors (GPP) with non-real time Operating Systems (OS). In this paper, we propose a BS architecture where most of the real-time processing is confined into a Virtual Hardware Enhancement Layer (VHEL). VHEL hides the hardware non-idealities from the software and vice versa. Possible errors due to the non-realtime OS and RRH appear as channel errors, which makes software development easier. We demonstrate the benefits of our architecture by implementing a Time-Division LTE system (TD-LTE) in C++ and running it as a user process in an Intel i7 class PC. Over-the-air transmissions are realized using USRPs. We report the performance of the implemented platform. We observe that with the given VHEL the transmitter and receiver never lose synchronization. Also the PC tends to be quick enough to feed the data; and the loss rate of subframes due to the non-real-time nature of the platform is relatively low. The proposed platform provides the possibility to implement TD-LTE on GPPs and virtual machines.

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