When various radio systems of the same type of Cognitive Radio Networks (CRNs) compete for channel resources, it becomes important to define some measures for them to coexist with the members of their own community, this is known as self-coexistence in literature. This paper studies self-coexistence by considering switching, interference, and channel quality as the three major impacting factors and thus presents the channel assignment algorithm (SwICh) for self coexistence in cognitive radio networks. This paper presents the assignment of blocks of channels (spectrum) available at various time periods, also known as time spectrum block (TSB) assignment. A set of access points (APs) or base stations (BSs), are allocated TSBs for data transmission by a centralized server. This server provides each AP a TSB based upon the three factors of switching, interference, and channel quality and their relative importance. When all the factors are equally important then all the three factors are given equal weights. When least switching is the goal, e.g. in real time applications such as Voice over Internet Protocol, it is important to avoid any kinds of delays, then switching can be given the highest weight. When interference is the major concern, as is in most coexistence scenarios, then interference can be given higher weight. When there is a huge channel quality variation, it is better to give channel quality a higher weight. Similarly their combinations can be utilized by changing their respective weights. These three factors are optimized by formulating a quadratic integer programming (QIP) problem over two time slots. This formulation is NP hard. To avoid the NP-hard complexity, we propose a near-optimal heuristic algorithm SwICh (Switching, Interference, and Channel Quality base Channel Allocation) that can be obtained at a much lower complexity. The SwICh algorithm offers near optimal solutions for TSB assignment.